[clang] [Clang][Diagnostics] Update select uses in DiagnosticXKinds.td to use enum_select (PR #130868)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

This one looks like a good candiate and the application is much clearer.

There are 2 comments (1 i think the name could be clearer, and the 2nd, we still need a newline at the end fo the file).

Else, let me know how you want to proceed.  We can rename this pull request to just rename this ONE (change the PR subject & message) and merge it, or we can wait for you to do quite a few at a time, your choice.

https://github.com/llvm/llvm-project/pull/130868