[clang] [libclang] Add clang_CXXMethod_getQualifiers and clang_Cursor_isConstexpr (PR #183305)

[Jannick Kremer via cfe-commits]

DeinAlptraum wrote:

Oh also before I forget again: please don't amend & force-push, it makes it harder to see what's changed and review accordingly.
(I know the Contribution guidelines say something about "a single commit", but that refers only to when you open the PR. Everything is squashed in the end before merging anyway, so no need to keep it clean)

https://github.com/llvm/llvm-project/pull/183305