Fix a crash produced when a pattern contains a BoxExpression as an element.

[mmatera]

This PR fixes a crash produced when a pattern contains a BoxExpression. Suppose for example that
we want to evaluate the expression

expr/.F[RowBox[list___]]->G[list] 

The pattern in the rule contains a RowBox, so in the evaluation, F[RowBox[list___]] is evaluated. Then, the RowBox[] expression is replaced by a RowBox object. Then, when Rule is evaluated, Pattern.create is called, with Expression(Symbol("Global`F"), RowBox(...)) as a parameter. It is not an Expression, so Patter.create fails raising an exception.

In this PR this behavior is fixed by catching this case and converting RowBox into an Expression before creating the pattern.

• Fix Pattern.create in a way that handles input expr that are not Atom or Expression, but have a to_expression method.
• Fix BoxExpression.sameQ to avoid infinite loops.
• adds the pattern_sort parameter to the BuiltinExpression.get_sort_key method.

[TiagoCavalcante]

LGTM

[rocky]

LGTM but a couple of comments. First it would be good to add a an example involving

expr/.F[RowBox[list___]]->G[list] 

so that it is clearer what is getting fixed.

Second there are these places where we don't have a pattern_sort parameter. Will any of these be a problem?

mathics/builtin/patterns.py:1670:    def get_sort_key(self) -> tuple:
mathics/core/element.py:150:    def get_sort_key(self) -> list:
mathics/core/evaluation.py:160:    def get_sort_key(self) -> Tuple[bool, bool, str]:
mathics/core/rules.py:110:    def get_sort_key(self) -> tuple:

[mmatera]

This seems to have been fixed in some other way, so let's close this.