[clang] [clang-format] Correctly annotate C# UTF 8 string literals (PR #211919)

[via cfe-commits]

================
@@ -455,6 +457,28 @@ bool FormatTokenLexer::tryMergeCSharpStringLiteral() {
   return true;
 }
 
+bool FormatTokenLexer::tryMergeCSharpUtf8StringLiteral() {
+  if (Tokens.size() < 2)
+    return false;
+
+  auto Suffix = Tokens.back();
+  if (Suffix->isNot(tok::identifier) || Suffix->TokenText != "u8")
----------------
owenca wrote:

```suggestion
  if (Suffix->TokenText != "u8")
```
This would work? Also, we should add "no whitespace before Suffix" so that `"foo" u8`, which is invalid C#, doesn't get merged.

https://github.com/llvm/llvm-project/pull/211919