[clang] Fix all mypy --strict errors in clang python binding (PR #101784)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

Thank you for your contribution! This is somewhat tricky situation, now that we have multiple opened PR in the same area of the codebase. But I think there is way forward:

1. https://github.com/llvm/llvm-project/pull/78114 and related work has been underway for several weeks, and I don't think anything should change there from the procedural standpoint. I encourage @TsXor to review it, and if you think something can be done better, feel free to leave a review. I also encourage @DeinAlptraum to take a look at this PR as it stands, and if you think this PR does something better than your work that is not yet merged, we can go with the approach here instead.

2. This PR is massive, which makes it hard to both review and, potentially, revert. As with https://github.com/llvm/llvm-project/pull/78114, I suspect that one can compile a list of fixes by topic that this PR covers. Items in such list are a good approximation of individual PRs that you should submit instead of this PR.

3. I see that >1k changed lines are tested by just 360 lines of code. This is sure a very rough estimate (sorry, I don't have time to review something this big right away), but it makes me wonder whether there's a room for more testing. 

https://github.com/llvm/llvm-project/pull/101784