`needsCapture` will ensure that any variables used within an async scope get included in the 'asyncScope' object that's created for that scope.
The variables used to lower Dart late variables in particular get emitted separately. But they can still be used across async scopes so they need the special capture logic as well.
Bug: https://github.com/dart-lang/sdk/issues/60748
Change-Id: I2486fce41f88f186fd799029c2cc59635f7ad8f5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/429780
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Commit-Queue: Nate Biggs <natebiggs@google.com>
Nate Biggs
e688981385