test.py invocations that specify a null safety mode will now work
without tool specific options.
For instance, `test.py --nnbd=strong -cdartkp -mrelease` will now add
the `non-nullable` experiment flag as well as the pass
`--sound-null-safety` to the relevant subcommands.
Fixes https://github.com/dart-lang/sdk/issues/42370
Change-Id: I1ae5bf569cc77ed6f26411c171c2cafe0a12eaff
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/164160
Reviewed-by: Bob Nystrom <rnystrom@google.com>
Commit-Queue: Alexander Thomas <athom@google.com>
Alexander Thomas
c34eef4fd8