[dev.typeparams] cmd/compile/internal/types2: adjusted array error message for compiler

Also: Triaged/adjusted some more test/fixedbugs tests.
Change-Id: Idaba1875273d6da6ef82dd8de8edd8daa885d32c
Reviewed-on: https://go-review.googlesource.com/c/go/+/276472


Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>