Feat/transitive deprecated ctors

[bzoracler]

This is a follow-on to #20104 (do not merge until #20104 has been merged). The relevant commits on top of #20104 are the last 2:

• 39e752f
• 0950c97

---

As mentioned in #20104 (comment) it is likely a good idea to report implicit usages of @deprecated() constructors in a callable-like context, e.g.

from collections.abc import Callable
from typing_extensions import deprecated

class A:
    @deprecated("do not use this")
    def __init__(self) -> None: ...

var: Callable[..., A] = A  # E: function A.__init__ is deprecated: do not use this

This PR supports this in the following contexts if the class constructor or one of its overloads is @deprecated() :

• The type context is Callable, a compatible callback protocol, or a union with at least 1 such item;
• The context location is an assignment, argument to a callable, or return value from a callable.

cc @sterliakov who initially suggested this expansion.

[bzoracler]

I did not want to add subtype checks for this case, as this seems like the most common case and at worst the user will get both a "deprecated" report and an "incompatible types in assignment" report.

[bzoracler]

In 0950c97 the same effect (avoiding false positives in the else branch of a conditional expression) could have also been implemented by doing this instead of having the boolean flag member self._valid_pep702_type_context:

with self.msg.filter_errors(filter_deprecated=not valid_pep702_type_context):
    ...

I chose not to do this because it would just compute the deprecation warnings, which involves subtype checking, and discard it without usage.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅