Bring back type annotation support of dunder methods in stub generator (fix #12717)

[bluenote10]

Have you read the Contributing Guidelines?

Yes.

Description

Fixes#12717 by making the "ignoring of dunder methods" more specific. As explained, __members__ is part of the official enum API and thus an essential type annotation to have. The complete removal of annotations of dunder methods in #12524 causes a big regression for pybind11 code bases involving lots of enums.

Test Plan

I didn't had time to add a specific test case preventing fully reverting #12524, but this modification should keep its behavior while fixing #12717.

[JelleZijlstra]

Could you take a look at the failing tests?

[bluenote10]

It basically what @shubz1998 already mentioned in comment #12524 (comment):

We can also choose to not ignore dunder methods in generate_c_property_stub, in that case, we would have to update the below two tests since these will now generate stubs for dunder attributes

As an alternative we can also just re-use the is_skipped_attribute function to filter out dunder properties. Then we would consistently avoid generating:

which seems to make sense.

With this change, the tests should need no adaptation, and relevant dunder methods like __member__ should still be generated.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉