[clang] [lldb] [clang][Sema] Split a err_typecheck_assign_const diagnostic into a separate tablegen entry (PR #179895)

[Corentin Jabot via cfe-commits]

https://github.com/cor3ntin approved this pull request.

LGTM
 You might want to use `%enum_select` to improve that further

https://github.com/llvm/llvm-project/pull/179895