Add extends of type parameter as type only location for completions

Fixes #28511

src/services/completions.ts

@@ -1129,6 +1129,9 @@ namespace ts.Completions {
 
                     case SyntaxKind.AsKeyword:
                         return parentKind === SyntaxKind.AsExpression;
+
+                    case SyntaxKind.ExtendsKeyword:
+                        return parentKind === SyntaxKind.TypeParameter;
                 }
             }
             return false;