[analyzer] Fix failing ParameterListTest cases.

These test cases were broken by
https://dart-review.googlesource.com/c/sdk/+/252566 and were marked
with `@failingTest`.

The reason for the breakage was that the aforementioned CL changed the
implementation of `AstComparator.visitSimpleFormalParameter` so that
it compared the parameter's names using `isEqualTokens` rather than
`isEqualNodes`. When this logic is used by `ParameterListTest`,
`isEqualTokens` and `isEqualNodes` are being overridden by methods in
the derived class `ResultComparator`, and one of the special behaviors
of `ResultComparator.isEqualNodes` is to allow the simple identifier
`_k_` to be substituted for a keyword token.

To fix the test, this special behavior needs to be moved from
`ResultComparator.isEqualNodes` to `ResultComparator.isEqualTokens`.

This paves the way for a follow-up CL in which I plan to rewrite
`ResultComparator` so that it doesn't depend on `AstComparator`; that
in turn will allow `AstComparator` to be rmoved.

Change-Id: I8434c7c694e1e5c613df62bf34ee69126fb0c2ec
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/418900
Reviewed-by: Konstantin Shcheglov <[email protected]>
Auto-Submit: Paul Berry <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: stereotype441

pkg/analyzer/test/src/fasta/recovery/missing_code_test.dart

@@ -565,7 +565,6 @@ f(a, _s_, b) {}
 ''');
   }
 
-  @failingTest
   void test_fieldFormalParameter_noPeriod_last() {
     testRecovery('''
 class C {
@@ -580,7 +579,6 @@ class C {
 ''');
   }
 
-  @failingTest
   void test_fieldFormalParameter_noPeriod_notLast() {
     testRecovery('''
 class C {

pkg/analyzer/test/src/fasta/recovery/recovery_test_support.dart

@@ -132,19 +132,20 @@ class ResultComparator extends AstComparator {
       if (first.isSynthetic && second.name == '_s_') {
         return true;
       }
-      if (first.token.isKeyword && second.name == '_k_') {
-        return true;
-      }
     }
     return super.isEqualNodes(first, second);
   }
 
   /// Overridden to ignore the offsets of tokens because these can legitimately
   /// be different.
   @override
-  bool isEqualTokensNotNull(Token first, Token second) =>
-      (first.isSynthetic && first.type == second.type) ||
-      (first.length == second.length && first.lexeme == second.lexeme);
+  bool isEqualTokensNotNull(Token first, Token second) {
+    if (first.isKeyword && second.lexeme == '_k_') {
+      return true;
+    }
+    return (first.isSynthetic && first.type == second.type) ||
+        (first.length == second.length && first.lexeme == second.lexeme);
+  }
 
   void _safelyWriteNodePath(StringBuffer buffer, AstNode? node) {
     buffer.write('  path: ');