Now moves mixin applications into their own libraries that can be
imported separately from the rest of the code in the originating
library.
Then adds an import to the new library containing the mixin application
to any libraries that use it.
This ensures the import graph is accurate while only making sure it
remains minimal.
TEST=Added case to pkg/vm testcases.
Bug: https://github.com/dart-lang/sdk/issues/43089
Change-Id: I56b6ea1db8261e0d0508c2d7e62d0c13fbe9678b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/457260
Reviewed-by: Alexander Markov <alexmarkov@google.com>
Commit-Queue: Nate Biggs <natebiggs@google.com>
Reviewed-by: Jens Johansen <jensj@google.com>
Nate Biggs
52be04e90a