Failures on Patterns parsing: improve error recovery for switch expressions.

[stereotype441]

There are new test failures on Patterns parsing: improve error recovery for switch expressions..

The tests

co19/LanguageFeatures/Patterns/type_inference_A22_t01 MissingCompileTimeError (expected Pass)

are failing on configurations

analyzer-asserts-linux
cfe-strong-linux
cfe-weak-linux

What's happening is that while parsing this code:

String test2() {
  num x = 0;
  return switch (x) {
    var y as INT => "int",
//           ^^^
// [analyzer] unspecified
// [cfe] unspecified
    final z as "String" => "String",
//             ^^^^^^^^
// [analyzer] unspecified
// [cfe] unspecified
    _ => "default";
  };
}

the improved parser error recovery is allowing _ => "default"; to be parsed (previously it was skipped). So the analyzer reports:

static error failures:
- Unexpected error at line 52, column 7, length 2: HINT.UNREACHABLE_SWITCH_CASE

- Unexpected error at line 52, column 19, length 1: SYNTACTIC_ERROR.EXPECTED_TOKEN

And the CFE reports:

static error failures:
- Unexpected error at line 52, column 19: Expected '}' before this.