Support Dart SDK main branch in recipes and modules

Bug: b/198416551
Change-Id: Ifc70d2aa84cb10e3a26474d1ae7658b3615eee7a
Reviewed-on: https://dart-review.googlesource.com/c/recipes/+/212571
Commit-Queue: Alexander Thomas <athom@google.com>
Reviewed-by: William Hesse <whesse@google.com>
42 files changed