Add support for PEP 702 (@deprecated)

[llucax]

Feature

Report where @deprecated symbols are used in the code.

Pitch

Python 3.12 is coming soon, and it introduces PEP 702 (the @deprecated decorator).mypy should support it.

[hauntsaninja]

(Technically PEP 702 will not be in Python 3.12, the PEP has not been accepted. But yes, mypy should support the draft standard and its use via typing_extensions)

[Bendabir]

If some people are interested, I wrote a small plugin to support this until it's part of mypy directly : https://github.com/Bendabir/mypypp

I don't really know the internals so it's probably a bit hacky but it appears to work.

[EwoutH]

If I'm correct, this issue is required for Python 3.13 support right? What's needed to move it forward?

[hauntsaninja]

You could make a PR that incorporates this feedback: #17476 (review)