go/types: list errors by default in TestManual

go/types: list errors by default in TestManual

This is a port of CL 315729 to go/types, adjusted for the slightly
different test set-up in go/types.

Added a TODO to reconcile these differences.

Change-Id: I71cae712d8fc23b7311ce35e09168b258e07fa35
Reviewed-on: https://go-review.googlesource.com/c/go/+/315850
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>