Add __hash__ stub to classes that are hashable and define __eq__

[TheTripleV]

Fixes #10424.

I only checked the types in builtins.pyi

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

prefect (https://github.com/PrefectHQ/prefect)
- src/prefect/utilities/templating.py:132: error: Incompatible types in assignment (expression has type "str", variable has type "dict[Any, Any]")  [assignment]
- src/prefect/utilities/templating.py:134: error: Incompatible types in assignment (expression has type "str", variable has type "dict[Any, Any]")  [assignment]
- src/prefect/utilities/templating.py:282: error: Incompatible types in assignment (expression has type "str", variable has type "dict[Any, Any]")  [assignment]
- src/prefect/utilities/templating.py:284: error: Incompatible types in assignment (expression has type "str", variable has type "dict[Any, Any]")  [assignment]

[AlexWaygood]

Thanks! Since #8465 didn't fix any known problems, however (just fixed some stylistic nits that we had), I'm inclined to revert the whole PR: see #10426. You're right that we missed this important detail of Python's semantics when it comes to determining whether an object is hashable or not :-)