cmd/compile/internal/types2: move a handful of tests

These tests belong into the fixedbugs directory.
This matches the go/types organization.
No changes to the code.

Change-Id: I36bcf70672d9ea5a40175c445e1d036c603ae76f
Reviewed-on: https://go-review.googlesource.com/c/go/+/312570


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