[vm/nnbd] Fix nullability of types in inferred types attribute
[vm/nnbd] Fix nullability of types in inferred types attribute

VM doesn't expect legacy nullability for Null type, so nullability
should be adjusted when writing AOT-specific inferred types attribute in
bytecode.

Change-Id: I58b09c9931f3cce6e70f661f1ba3e7e015e7f739
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/127985
Reviewed-by: Régis Crelier <c2bf536a10d9f2530c38e4e8da517718be8c39ce@google.com>
Commit-Queue: Alexander Markov <239e774fd29abc1267878f57afe1a8a03e0ca887@google.com>

dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk