1d6a7bee36
This generalizes the dartfix NNBD processing of packages so that other fixes can process packages in a similar manner. In addition, if at least one package to be migrated to NNBD cannot be marked as NNBD or is not already NNBD, then no additional NNBD processing is done. This also addresses comments in https://dart-review.googlesource.com/c/sdk/+/98429 Change-Id: I406d9d395a0ee8a85cc5b3d7be311a76e1e48bdb Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/98524 Reviewed-by: Brian Wilkerson <brianwilkerson@google.com> Commit-Queue: Dan Rubel <danrubel@google.com>