[clang-format] Correctly detect `!` as TT_NonNullAssertion after `default`.

[curdeius]

Summary

Fixes https://github.com/llvm/llvm-project/issues/53153.

Depends on D121132.

[curdeius]

Add test from the bug report.

clang/lib/Format/TokenAnnotator.cpp

if ((Style.isJavaScript() || Style.isCSharp()) &&
       if (Current.Previous) {
         bool IsIdentifier =
             Style.isJavaScript()
                 ? Keywords.IsJavaScriptIdentifier(
                       *Current.Previous, /* AcceptIdentifierName= */ true)
                 : Current.Previous->is(tok::identifier);
         if (IsIdentifier ||
             Current.Previous->isOneOf(
-                tok::kw_namespace, tok::r_paren, tok::r_square, tok::r_brace,
-                tok::kw_false, tok::kw_true, Keywords.kw_type, Keywords.kw_get,
-                Keywords.kw_init, Keywords.kw_set) ||
+                tok::kw_default, tok::kw_namespace, tok::r_paren, tok::r_square,
+                tok::r_brace, tok::kw_false, tok::kw_true, Keywords.kw_type,
+                Keywords.kw_get, Keywords.kw_init, Keywords.kw_set) ||
             Current.Previous->Tok.isLiteral()) {
           Current.setType(TT_NonNullAssertion);
           return;
         }
       }
       if (Current.Next &&
           Current.Next->isOneOf(TT_BinaryOperator, Keywords.kw_as)) {
         Current.setType(TT_NonNullAssertion);

clang/unittests/Format/FormatTestCSharp.cpp

class TimePeriod {
   verifyFormat(R"(//
 public class SaleItem
 {
     public decimal Price { get; set; }
 })",
                MicrosoftStyle);
 }
 
+TEST_F(FormatTestCSharp, DefaultLiteral) {
+  FormatStyle Style = getGoogleStyle(FormatStyle::LK_CSharp);
+
+  verifyFormat(
+      "T[] InitializeArray<T>(int length, T initialValue = default) {}", Style);
+  verifyFormat("System.Numerics.Complex fillValue = default;", Style);
+  verifyFormat("int Value { get } = default;", Style);
+  verifyFormat("int Value { get } = default!;", Style);
+}
+
 TEST_F(FormatTestCSharp, CSharpSpaces) {
   FormatStyle Style = getGoogleStyle(FormatStyle::LK_CSharp);
   Style.SpaceBeforeSquareBrackets = false;
   Style.SpacesInSquareBrackets = false;
   Style.SpaceBeforeCpp11BracedList = true;
   Style.Cpp11BracedListStyle = false;
   Style.SpacesInContainerLiterals = false;
   Style.SpaceAfterCStyleCast = false;