This create a stub for combined member signatures from multiple
inherited non-extension type members and adds these to the
extension type declaration.
A sealed [TypeDeclaration] superclass is added to [Class] and
[ExtensionTypeDeclaration] to support accessing the enclosing type
declaration from a [Member].
TEST=existing
Change-Id: Ic01535d27a14187d37b00868e7e90fe73558b051
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/331181
Commit-Queue: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Slava Egorov <vegorov@google.com>
Reviewed-by: Chloe Stefantsova <cstefantsova@google.com>
Johnni Winther
e06536af2e