[augmentations] No error when augmenting class-like declaration named augmented

[sgrekhov]

In an augmentation scope augmented is a reserved world and can be used for calling introductory declaration only. Any other use of this word is a compile-time error. But there is no expected error in the analyzer below

class augmented {}

augment class augmented {}
//            ^^^^^^^^^
// [analyzer] unspecified
// [cfe] unspecified

main() {
  print(augmented);
}

Appropriate cp19 tests:
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t14.dart
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t15.dart
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t16.dart
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t17.dart
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Augmentation-libraries/augmented_expression_A09_t18.dart

[sgrekhov]

The same for the type variable named augmented, superclass ets.

class C<augmented> {}

augment C<augmented> {}

Tests
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Augmentation-libraries/augmented_expression_A10_t24.dart
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Augmentation-libraries/augmented_expression_A10_t25.dart
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Augmentation-libraries/augmented_expression_A10_t26.dart
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Augmentation-libraries/augmented_expression_A10_t27.dart
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Augmentation-libraries/augmented_expression_A10_t28.dart
https://github.com/dart-lang/co19/blob/master/LanguageFeatures/Augmentation-libraries/augmented_expression_A10_t29.dart