[Sema] Add -Wc++11-narrowing-const-reference (#76094)

https://github.com/llvm/llvm-project/pull/75332 diagnosed narrowing
involving const reference. Our depot has hundreds if not thousands of
breakages

(https://github.com/llvm/llvm-project/pull/75332#issuecomment-1864757240).
Add a subgroup of -Wc++11-narrowing to help users gradually fix their
issues without regressing the existing -Wc++11-narrowing diagnostics.