[clang] [Clang][TableGen] Use const pointers for various Init objects in Diagnostic Emitter (PR #112318)

[Kazu Hirata via cfe-commits]

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

LGTM with the `const auto *` suggestion from @erichkeane .

https://github.com/llvm/llvm-project/pull/112318