[clang] [libclang] Add API to query more information about base classes. (PR #120300)

[Trevor Laughlin via cfe-commits]

trelau wrote:

For what it's worth, to get around my issue in https://github.com/llvm/llvm-project/issues/121502 I followed your same pattern here and added a ```get_methods()``` function to Python (and a new libclang function ```clang_visitCXXMethods```) to access the class methods.

Looking at [CXXRecordDecl](https://clang.llvm.org/doxygen/classclang_1_1CXXRecordDecl.html), perhaps the following might all be useful to add to the libclang API (including Python):
- methods()
- fields()
- ctors()?
- friends()?

For my purposes of parsing C++ headers and generating Python bindings via pybind11, this bases PR plus adding the ```get_methods()``` function would make things much easier (ctors and friends seem like more "nice to have" and ctors seem to come through in "methods" anyway and can be determined by the cursor kind property).

Adding ```get_methods``` was basically copy/pasting your work (see libclang function [here](https://github.com/llvm/llvm-project/issues/121502#issuecomment-2571512174)).

I'll open a PR for the ```get_methods()``` addition (and maybe I'll try the others if they work as I imagine them to).

https://github.com/llvm/llvm-project/pull/120300