NFC: Clean up of IntrusiveRefCntPtr construction from raw pointers. (#151545)

Handles clang::DiagnosticsEngine and clang::DiagnosticIDs.

For DiagnosticIDs, this mostly migrates from `new DiagnosticIDs` to
convenience method `DiagnosticIDs::create()`.

Part of cleanup https://github.com/llvm/llvm-project/issues/151026

NOKEYCHECK=True
GitOrigin-RevId: c7f343750744fd0c928b1da67e9dd894a2fe52cf
1 file changed