Add libclang function `clang_isBeforeInTranslationUnit` to allow checking the order between two source locations.
Simplify the `SourceRange.__contains__` implementation using this new function.
Add tests for `SourceRange.__contains__` and the newly added functionality.
Fixes#22617Fixes#52827
The `Index.h` header defines some functions and data structures that are useful for other (non-indexing) APIs. This patch extracts those into separate headers.
Reviewed By: akyrtzi, benlangmuir
Differential Revision: https://reviews.llvm.org/D134837