[vm] Fix yield in async* to check if the stream was canceled while generator was suspended

Previously there was a window between the decision to resume generator
and actually running the micro-task. The stream could be canceled
during that window, making running the generator incorrect.

The solution is to check if the stream was canceled right before
resuming the generator in yield/yield*.

This change also unifies yield and yield* to check if the stream
was canceled even before suspending the generator.

TEST=language/async_star/cancel_while_paused_test,
language/async_star/cancel_while_paused_at_yield_test

Fixes https://github.com/dart-lang/sdk/issues/49451

Change-Id: Ib8ff3a2da9a6a7da8766a7dbf28e2c9d618728f9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/251562
Commit-Queue: Alexander Markov <alexmarkov@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>