Migration: fix pubspec deps.
Migration: fix pubspec deps.

The previous deps had never been validated and were wrong in many ways
(for some deps the constraint was too narrow or too wide; other deps
were missing or extraneous).  I did some experimenting with `pub get`
and `pub run test` to find the earliest version of each package for
which the version solve succeeds and the tests pass.

Note, however, that nnbd_migration currently depends on unpublished
functionality from the _fe_analyzer_shared and analyzer packges.  So
before publishing nnbd_migration we'll need to publish
_fe_analyzer_shared and analyzer and then update the pubspec one last
time.

Change-Id: If8453226bfcc5e94ac84f1a3fdc0d2f4ee150f54
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149661
Reviewed-by: Samuel Rawlins <5cf2cac5eec2ad6d0eb2b0f4ff6af9a590ce2bf6@google.com>
Commit-Queue: Paul Berry <72d414e3a99fb120308437779d51667bcc0984eb@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk