[clang] [libclang] Fix clang_CXXMethod_isDeleted for functions (PR #183286)

[via cfe-commits]

Serafean wrote:

Unfortunately now the `clang_CXXMethod_isDeleted` name will be a bit misleading. 

Solutions I see:
- keep this one as is (deprecate it?) and introduce `clang_CXX_isDeleted`
- introduce `clang_CXX_isDeleted` and alias it to `clang_CXXMethod_isDeleted`

Any other ideas welcome.

https://github.com/llvm/llvm-project/pull/183286