[clang] [libclang/python] Add LIBCLANG_LIBRARY_PATH and LIBCLANG_LIBRARY_FILE (PR #170201)

[Vlad Serebrennikov via cfe-commits]

https://github.com/Endilll commented:

I'm not a fan of the existing terminology in this part of our codebase, where "path" should be understood as "search path" or "containing directory", while "file" and "filename" are "path to the file" (probably a full path, but that is yet to be confirmed). I left couple of suggestions that should improve the clarity of the error message and the release note.

That's probably out of scope here, but I'd like to see `Config.library_path`, `Config.library_file`, `Config.get_filename` to be renamed to something less confusing. As for `LIBCLANG_LIBRARY_PATH`, it can be argued that it follows a well-established example of `LD_LIBRARY_PATH`, so I can live with this.

https://github.com/llvm/llvm-project/pull/170201