[VM/nnbd] Do not increase length of a list of non-nullable elements.
[VM/nnbd] Do not increase length of a list of non-nullable elements.

This fixes the VM implementation of _GrowableList.insert() (fixes #40913)
and of _GrowableList.insertAll()

Change-Id: I1bcbe1bd56c2da482c31aa9311b65b2fb683b1b2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/139563
Commit-Queue: Régis Crelier <c2bf536a10d9f2530c38e4e8da517718be8c39ce@google.com>
Reviewed-by: Siva Annamalai <2e618a8cbd7bb6b3d4409061ae407d692a098546@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