remove incorrect diagnostic for invalid python identifier in dataclass field aliases and prevent them from appearing in completions

[DetachHead]

fixes #837

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

sympy (https://github.com/sympy/sympy)
-   /tmp/mypy_primer/projects/sympy/sympy/stats/compound_rv.py:107:9 - warning: Return type, "tuple[Unknown, ...] | Unknown | Self@Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | Sum | Integral | None", is partially unknown (reportUnknownParameterType)
+   /tmp/mypy_primer/projects/sympy/sympy/stats/compound_rv.py:107:9 - warning: Return type, "tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | Integral | None", is partially unknown (reportUnknownParameterType)
-     Type of "compute_expectation" is "(expr: Unknown, rvs: Unknown | None = None, **kwargs: Unknown) -> (tuple[Unknown, ...] | Unknown | Self@Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | Sum | None)" (reportUnknownMemberType)
+     Type of "compute_expectation" is "(expr: Unknown, rvs: Unknown | None = None, **kwargs: Unknown) -> (tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | None)" (reportUnknownMemberType)
-   /tmp/mypy_primer/projects/sympy/sympy/stats/compound_rv.py:113:20 - warning: Return type, "tuple[Unknown, ...] | Unknown | Self@Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | Sum | None", is partially unknown (reportUnknownVariableType)
+   /tmp/mypy_primer/projects/sympy/sympy/stats/compound_rv.py:113:20 - warning: Return type, "tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | None", is partially unknown (reportUnknownVariableType)
-     Type of "doit" is "((**hints: Unknown) -> Equality) | Unknown | ((**hints: Unknown) -> Relational) | ((**hints: Unknown) -> Unequality) | ((**hints: Unknown) -> (tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | None)) | ((**hints: Unknown) -> Unknown)" (reportUnknownMemberType)
+     Type of "doit" is "((**hints: Unknown) -> Equality) | Unknown | ((**hints: Unknown) -> Relational) | ((**hints: Unknown) -> Unequality) | ((**hints: Unknown) -> (tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | None)) | ((**hints: Unknown) -> Unknown)" (reportUnknownMemberType)
-     Type of "summation" is "(f: Unknown, ...) -> (Equality | Relational | Unequality | Unknown)" (reportUnknownVariableType)
+     Type of "summation" is "(f: Unknown, ...) -> (tuple[Unknown, ...] | Unknown | Self@Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | None)" (reportUnknownVariableType)
-     Type of "density" is "(expr: Unknown, condition: Unknown | None = None, evaluate: bool = True, numsamples: Unknown | None = None, **kwargs: Unknown) -> (dict[Unknown, Unknown] | Density | Lambda | Basic | Any | Unknown | FiniteDensity | None)" (reportUnknownVariableType)
+     Type of "density" is "(expr: Unknown, condition: Unknown | None = None, evaluate: bool = True, numsamples: Unknown | None = None, **kwargs: Unknown) -> Unknown" (reportUnknownVariableType)
-   /tmp/mypy_primer/projects/sympy/sympy/stats/drv.py:242:13 - warning: Type of "dens" is partially unknown
+   /tmp/mypy_primer/projects/sympy/sympy/stats/drv.py:242:13 - warning: Type of "dens" is unknown (reportUnknownVariableType)
-     Type of "dens" is "dict[Unknown, Unknown] | Density | Lambda | Basic | Any | Unknown | FiniteDensity | None" (reportUnknownVariableType)
+   /tmp/mypy_primer/projects/sympy/sympy/stats/drv.py:245:53 - warning: Argument type is unknown
+     Argument corresponds to parameter "pdf" in function "__new__" (reportUnknownArgumentType)
-     Type of "doit" is "Unknown | ((**hints: Unknown) -> (tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | None)) | ((**hints: Unknown) -> Self@Expr) | ((**hints: Unknown) -> Order) | Any | ((**hints: Unknown) -> Piecewise) | ((**hints: Unknown) -> Basic) | ((**hints: Unknown) -> Equality) | ((**hints: Unknown) -> Relational) | ((**hints: Unknown) -> Unequality)" (reportUnknownMemberType)
+     Type of "doit" is "Unknown | ((**hints: Unknown) -> (tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | None)) | ((**hints: Unknown) -> Self@Expr) | ((**hints: Unknown) -> Order) | Any | ((**hints: Unknown) -> Piecewise) | ((**hints: Unknown) -> Basic) | ((**hints: Unknown) -> Equality) | ((**hints: Unknown) -> Relational) | ((**hints: Unknown) -> Unequality)" (reportUnknownMemberType)
-     Type of "probability" is "(condition: Unknown) -> Unknown" (reportUnknownMemberType)
+     Type of "probability" is "(condition: Unknown) -> (Unknown | Probability | Self@Expr | tuple[Unknown, ...] | Sum | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | int)" (reportUnknownMemberType)
-     Type of "doit" is "((**hints: Unknown) -> Equality) | Unknown | ((**hints: Unknown) -> Relational) | ((**hints: Unknown) -> Unequality) | ((**hints: Unknown) -> (tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | None))" (reportUnknownMemberType)
+     Type of "doit" is "((**hints: Unknown) -> Equality) | Unknown | ((**hints: Unknown) -> Relational) | ((**hints: Unknown) -> Unequality) | ((**hints: Unknown) -> (tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | None))" (reportUnknownMemberType)
-     Type of "doit" is "((**hints: Unknown) -> Equality) | Unknown | ((**hints: Unknown) -> Relational) | ((**hints: Unknown) -> Unequality) | ((**hints: Unknown) -> (tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | None))" (reportUnknownMemberType)
+     Type of "doit" is "((**hints: Unknown) -> Equality) | Unknown | ((**hints: Unknown) -> Relational) | ((**hints: Unknown) -> Unequality) | ((**hints: Unknown) -> (tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | None))" (reportUnknownMemberType)
-   /tmp/mypy_primer/projects/sympy/sympy/stats/frv.py:443:9 - warning: Return type, "tuple[Unknown, ...] | Unknown | Self@Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | Sum | None", is partially unknown (reportUnknownParameterType)
+   /tmp/mypy_primer/projects/sympy/sympy/stats/frv.py:443:9 - warning: Return type, "tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | None", is partially unknown (reportUnknownParameterType)
-     Type of "doit" is "((**hints: Unknown) -> Equality) | Unknown | ((**hints: Unknown) -> Relational) | ((**hints: Unknown) -> Unequality) | ((**hints: Unknown) -> (tuple[Unknown, ...] | Unknown | Self@Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | Sum | None))" (reportUnknownMemberType)
+     Type of "doit" is "((**hints: Unknown) -> Equality) | Unknown | ((**hints: Unknown) -> Relational) | ((**hints: Unknown) -> Unequality) | ((**hints: Unknown) -> (tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | None))" (reportUnknownMemberType)
-   /tmp/mypy_primer/projects/sympy/sympy/stats/frv.py:451:20 - warning: Return type, "tuple[Unknown, ...] | Unknown | Self@Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | Sum | None", is partially unknown (reportUnknownVariableType)
+   /tmp/mypy_primer/projects/sympy/sympy/stats/frv.py:451:20 - warning: Return type, "tuple[Unknown, ...] | Unknown | Sum | Self@Expr | Order | Any | Piecewise | Basic | Equality | Relational | Unequality | None", is partially unknown (reportUnknownVariableType)
-   /tmp/mypy_primer/projects/sympy/sympy/stats/frv_types.py:236:16 - error: Operator "&" not supported for types "_NotImplementedType | GreaterThan | Unknown | Equality | Relational | Unequality" and "_NotImplementedType | LessThan | Unknown | Equality | Relational | Unequality"
-     Operator "&" not supported for types "GreaterThan" and "LessThan"
-     Operator "&" not supported for types "GreaterThan" and "Equality"
-     Operator "&" not supported for types "GreaterThan" and "Relational"
-     Operator "&" not supported for types "GreaterThan" and "Unequality"
-     Operator "&" not supported for types "Equality" and "LessThan"
-     Operator "&" not supported for types "Equality" and "Equality"
-     Operator "&" not supported for types "Equality" and "Relational"
-     Operator "&" not supported for types "Equality" and "Unequality"
-     ... (reportOperatorIssue)
-   /tmp/mypy_primer/projects/sympy/sympy/stats/frv_types.py:425:16 - error: Operator "&" not supported for types "_NotImplementedType | GreaterThan | Unknown | Equality | Relational | Unequality" and "_NotImplementedType | LessThan | Unknown | Equality | Relational | Unequality"
-     Operator "&" not supported for types "GreaterThan" and "LessThan"
-     Operator "&" not supported for types "GreaterThan" and "Equality"
-     Operator "&" not supported for types "GreaterThan" and "Relational"
-     Operator "&" not supported for types "GreaterThan" and "Unequality"
-     Operator "&" not supported for types "Equality" and "LessThan"
-     Operator "&" not supported for types "Equality" and "Equality"
-     Operator "&" not supported for types "Equality" and "Relational"
-     Operator "&" not supported for types "Equality" and "Unequality"
-     ... (reportOperatorIssue)
-   /tmp/mypy_primer/projects/sympy/sympy/stats/frv_types.py:713:17 - error: Operator "&" not supported for types "_NotImplementedType | GreaterThan | Unknown | Equality | Relational | Unequality" and "_NotImplementedType | LessThan | Unknown | Equality | Relational | Unequality"

... (truncated 409 lines) ...

asynq (https://github.com/quora/asynq): 212.37x slower (0.1s -> 13.1s in a single noisy sample)