[nnbd_migration] Unwrap legacy member elements into their NNBD declarations
[nnbd_migration] Unwrap legacy member elements into their NNBD declarations

Change-Id: I4a2d445625716a61c00f970f04a95af8aaa918fb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/128101
Commit-Queue: Mike Fairhurst <2002604e76601be549134505841fea93de80dc45@google.com>
Reviewed-by: Brian Wilkerson <1f7641b6b14c52b9163524ab8d9aabff80176f21@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