Add ClassOrAugmentationDeclaration, ClassAugmentationDeclaration.
Add ClassOrAugmentationDeclaration, ClassAugmentationDeclaration.

Change-Id: I274a8ad06b7cd334623fd13ff47b5eb632232c45
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/253060
Reviewed-by: Brian Wilkerson <1f7641b6b14c52b9163524ab8d9aabff80176f21@google.com>
Commit-Queue: Konstantin Shcheglov <09e4d7516628963212bf4aace2f97603d2b706e4@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk