go/types, types2: better error message when type argument cannot use operator

go/types, types2: better error message when type argument cannot use operator

Fixes #63524

Change-Id: Id33936b9bcfb6a7333c6d084247044bba2f29219
Reviewed-on: https://go-review.googlesource.com/c/go/+/613756
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>