Fix various small issues
Fix various small issues

This CL makes a lot of small corrections in enhanced_enums_basic_test,
e.g., references to variables whose name is slightly different in the
declaration and at the use site.

[Edit: This CL no longer adds a new test, `enhanced_enums_error_test`
already covers all the situations tested by that new test.]

Change-Id: I9d2aabd5ab740b91463eff12a5c676136bf4ec04
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/233384
Reviewed-by: Lasse Nielsen <80295e4ef244a07779f93eaa95d582bad8e316a5@google.com>
Commit-Queue: Erik Ernst <251bb01623bfda2cd9151e339a6e783ca432874c@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk