[clang] [clang][diagnostics] Refactor "warn_doc_function_method_decl_mismatch" to use enum_select (PR #146426)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

Please see the comment by the bot about your email address and fix that please.

https://github.com/llvm/llvm-project/pull/146426