Change null-aware `operator []`, `operator []=`, and function call to not have a period.
Change null-aware `operator []`, `operator []=`, and function call to not have a period.

Change-Id: I8b9c83e216dd713afeef8a1c1cf93c36c8de3792
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/132840
Reviewed-by: Lasse R.H. Nielsen <80295e4ef244a07779f93eaa95d582bad8e316a5@google.com>
Commit-Queue: Erik Ernst <251bb01623bfda2cd9151e339a6e783ca432874c@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