[clang] [clang] Improve diagnostics for invalid named-universal-characters (PR #206326)

[Timm Baeder via cfe-commits]

================
@@ -539,6 +539,10 @@ static bool ProcessNumericUCNEscape(const char *ThisTokBegin,
   return !HasError;
 }
 
+static bool AllowedInCharacterName(char C) {
----------------
tbaederr wrote:

Functions should start lowercase: https://llvm.org/docs/CodingStandards.html#name-types-functions-variables-and-enumerators-properly

https://github.com/llvm/llvm-project/pull/206326