Expose deprecations using PEP 702

[jtojnar]

There is now PEP 702 – Marking deprecations using the type system, which might be useful for updating deprecated code.

[lovetox]

@mat-xc do you know if the introspection files contain the information if the method is deprecated?

[jtojnar]

GI.BaseInfo.is_deprecated() method is what PyGObject itself uses.