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

[Michael Buch via cfe-commits]

Michael137 wrote:

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

Ah nice didn't know about `enum_select`

The enum is currently unnamed and local to `SemaExpr` so we'd have to move it out some header, name it, etc. So to keep the diff small I'll leave that for possible follow-up

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