Roll dart_style 2.2.2 into the repo.

This adds formatting support for upcoming language features:

- Named arguments anywhere
- Enhanced enums
- "super." parameters

It doesn't change the formatting of any existing code, so it should be
safe to roll this in without coordinating a pre-built SDK roll.

I also went ahead and ran the formatter on the related language tests
since before now they couldn't be formatted. (And I incidentally ran
the formatter on the other enum tests sitting in the same directory.)

Edit: Actually there is one small change to existing formatting: enum
declarations will now get a blank line inserted before them. Most hand
authored enums already have this so will be unchanged but I see a few
diffs when formatting generated code.

Change-Id: Icefd9f10bedc589312396cf0ddb8eafc418f8dbf
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/235284
Auto-Submit: Bob Nystrom <rnystrom@google.com>
Reviewed-by: Alexander Thomas <athom@google.com>
Reviewed-by: William Hesse <whesse@google.com>
Commit-Queue: William Hesse <whesse@google.com>