[clang] [NFC][Clang] Use StringRef instead of string in ClangDiagnosticEmitter (PR #115959)

[Rahul Joshi via cfe-commits]

================
@@ -145,7 +146,7 @@ static bool diagGroupBeforeByName(const Record *LHS, const Record *RHS) {
          RHS->getValueAsString("GroupName");
 }
 
-using DiagsInGroupTy = std::map<std::string, GroupInfo, std::less<>>;
+using DiagsInGroupTy = std::map<StringRef, GroupInfo, std::less<>>;
----------------
jurahul wrote:

Done.

https://github.com/llvm/llvm-project/pull/115959