The added field holds the interface signature type for a Procedure when
this is different from the class signature type (implied by the function
parameters and return type). This is needed for forwarding semi stubs
when its declared type is different from the called super member.
Closes https://github.com/dart-lang/sdk/issues/47072
TEST=pkg/front_end/testcases/general/implement_semi_stub.dart and more
Change-Id: I4a7cdc9d564fb0a59e7b06e83646b5410d8d82f5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/216420
Commit-Queue: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Chloe Stefantsova <dmitryas@google.com>
Johnni Winther
56490f9776