[Dot Shorthands] Language Tests in `tests/language`

[kallentu]

Write up language tests for the tests/language repository.

Test Tracker

https://docs.google.com/spreadsheets/d/19L0AhfQjS4VjvkdQ1lz61SZhK_nGjuPzs6OODEUyPx0/edit?usp=sharing&resourcekey=0-UwYFyigOGgtphjW50XztsQ

[dart-github-bot]

Summary: The issue requests the addition of language tests for enum shorthands in the tests/language repository. The tests are currently in progress and depend on the final specification for enum shorthands.