Linux watcher: moves between directories cause incorrect events

[davidmorgan]

Due to dart-lang/sdk#62014 the events arrive out of order and this can cause incorrect reporting.

For example a move into a directory immediately followed by a delete causes incorrect reporting because the events arrive out of order and the delete is ignored.

This was caught due to different random e2e testing in the google3 roll(!), I'm in process of adding test coverage for it over at #2248