`test`/`group` wrap with and similar assists

[FMorschel]

Similar to the Flutter's Wrap with Foo assists or Remove Widget, I think we could do similar ones for test and group. Since there are fewer cases than widgets, I think this will be an easy way to handle the already existing test cases and will complement nicely with our snippets for test and group.

CC @bwilkerson @DanTup @srawlins

[bwilkerson]

A 'Wrap with test' assist doesn't make sense.

A 'Wrap with group' potentially makes sense, as does a 'Remove group', but I have to wonder how much value they would add.

I'm not sure what other "similar" assists you're thinking about.

[FMorschel]

I was imagining:

• Wrap with group
• Wrap with test (on expect or some similar statement(/statement list) in a _test.dart file could be valid, but I agree less useful)
• Remove group/test (for when you clone part of a test file for similar tests)
• Move test/group up/down