[clang] [libclang/python] Derive library function types from annotations (PR #142120)

[Vlad Serebrennikov via cfe-commits]

Endilll wrote:

Good news: typeshed has annotations for ctypes, and they have annotations for `_CPointer` that might come helpful for us:
https://github.com/python/typeshed/blob/b25a5b6aef4b18226a9fd367421ed8ebaaed9528/stdlib/_ctypes.pyi#L76-L87

Bad news: they admit that they can't model implicit `c_int` to `int` conversions that ctypes implementation does:
https://github.com/python/typeshed/blob/b25a5b6aef4b18226a9fd367421ed8ebaaed9528/stdlib/_ctypes.pyi#L155-L166

https://github.com/llvm/llvm-project/pull/142120