[clang] [clang][Python] Apply type annotations to Python (PR #173845)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

Thank you for the effort!
I see some useful and less useful things in here, and it'd make sense to separate them to facilitate reviews.
I consider annotations on parameters and return types of user-facing functions definitely useful.
The rest are more questionable to me, so I'd like to see justification for them.

https://github.com/llvm/llvm-project/pull/173845