[clang] [libclang/python] Fix some type errors, add type annotations (PR #98745)

[Vlad Serebrennikov via cfe-commits]

https://github.com/Endilll approved this pull request.

Looks good aside from missing release notes, especially entries to potentially breaking changes.
Given that you've been making a significant amount of changes to Python bindings that are spread over multiple PRs, it's worth considering if 19 release branching on Tuesday, 23rd of July is of any significance for this effort. If you think that broken or half-baked things are going into 19 branch, reach out to me or Aaron on `#clang` channel on our Discord server. We can both pull things out, or cherry-pick changes from `main` into `releases/19.x`, as long as we do it in a timely manner.

https://github.com/llvm/llvm-project/pull/98745