[clang] [clang][diagnostics] Refactor "warn_doc_api_container_decl_mismatch" to use enum_select (PR #146433)

[Corentin Jabot via cfe-commits]

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

thanks. will you need us to merge that for you?

https://github.com/llvm/llvm-project/pull/146433