[analyzer] rewrite mostSpecificTypeArgument to use asInstanceOf
[analyzer] rewrite mostSpecificTypeArgument to use asInstanceOf

Change-Id: If7c9e9e9cdc1999c6f7d3c74d081a457f9fc229e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/97278
Auto-Submit: Mike Fairhurst <2002604e76601be549134505841fea93de80dc45@google.com>
Reviewed-by: Konstantin Shcheglov <09e4d7516628963212bf4aace2f97603d2b706e4@google.com>
Commit-Queue: Mike Fairhurst <2002604e76601be549134505841fea93de80dc45@google.com>

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