Fixes for Julia nightly

[serenity4]

Makes Diffractor functional on nightly, ensuring that the test suite runs without errors.

Requires JuliaDiff/ChainRules.jl#819 merged and JuliaDebug/Cthulhu.jl#621 released to be fully functional.

Before merge (marking as draft until completed, but this is ready for review):

• Have both dependent PRs merged and a new version released for Cthulhu and ChainRules.
• Raise the compat bound for Cthulhu to 2.6.13 (we use the function set_cthulhu_source! introduced in adjust Cthulhu to JuliaLang/julia#56248 JuliaDebug/Cthulhu.jl#621 for convenience).
• Figure out how to version Compiler or use Base.Compiler (see Fixes for Julia nightly #300 (comment))

A significant refactor of the overload of CC.finishinfer!/CC.finish!/CC.transform_result_for_cache was made to follow exactly the same logic as Cthulhu (these seem to have been copy-pasted from there into Diffractor, the changes simply sync them).

The most notable change in this PR is that it works around IR changes, as described below.

GlobalRef changes

On nightly, what used to be a GlobalRef in lowered IR may now be a getproperty instead, with a first Module SSA argument and a symbol. To illustrate this, instead of something like

%1 = B.x

we now have

%1 = Main.B
%2 = getproperty(%1, :x)

As a possible fix, we may preserve the old semantics by associating the latter IR with the former. This is what I attempted to fix the failing tests, but as the IR transforms are performed within a generated function we cannot evaluate GlobalRefs for module arguments (as in Main.B) to know whether getproperty is a global access or not (i.e. is the first argument a module), because we can't see past the world age of the generated function definition.

Instead, we instrument the getproperty call for differentiation, and I added a rrule with NoTangent().

[serenity4]

This will also need a proper Compiler versioning. I went with deving the path in my Julia nightly installation, perhaps we can revert to using Base.Compiler instead of relying on the package to keep things in sync.

EDIT: this is discussed at JuliaLang/julia#57520

[serenity4]

There is a severe limitation to this; because we call this within a generated function, it can only see bindings that have been defined before the generated function. Even if one were to be defined, any redefinitions would not invalidate the generated IR, which is quite bad.

I believe the real solution would be to stop using generated functions, and perhaps use an AbstractInterpreter with invoke(f, ::CodeInstance, args...) so we can properly resolve globals and use interpreter caching with invalidation edges attached as appropriate.

[serenity4]

Changed that in ac7bce4 to use rrule instead for now, so we can keep the current generated function setup.