[clang] [clang] Add covariance tests that make sure we return an error when return value is different in pointer / lvalue ref / rvalue ref (PR #112853)

[Vlad Serebrennikov via cfe-commits]

https://github.com/Endilll approved this pull request.

Thank you! This is good to go now.

https://github.com/llvm/llvm-project/pull/112853