This package tests the language versioning infrastructure, in
particular how it interacts with imports, exports, and part
files. With the removal of legacy (pre-2.12) support from Dart, we
need the tests in this package to use newer language versions.
Change-Id: I415307a8e644c756da649d7d51da860b5b37de7b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/341022
Reviewed-by: Jake Macdonald <jakemac@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
