[vm] Ignore experimental_member_use in tests of @RecordUse.

I will shortly be adding functionality to the analyzer to issue an
`experimental_member_use` warning when an element annotated with
`@experimental` is referenced. Since `@RecordUse` is currently
annotated with `@experimental`, we will need to ignore this warning
when testing it.

Tested: standard trybots
Change-Id: I6a6a6964293b7976c25121e4eb38bc9652501599
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/450973
Reviewed-by: Alexander Markov <[email protected]>
Commit-Queue: Paul Berry <[email protected]>

Author: stereotype441

pkg/vm/testcases/transformations/analysis_options.yaml

@@ -5,6 +5,8 @@
 analyzer:
   errors:
     sdk_version_since: ignore
+    # `@RecordUse` is still experimental.
+    experimental_member_use: ignore
   exclude:
     - deferred_loading/**
     - dynamic_interface_annotator/**