go/types: expand is only required for *Named types

go/types: expand is only required for *Named types

This is a port of CL 340749 to go/types.

Change-Id: I2af602d357486ee2f45b91c11c4b02ec6b58ed38
Reviewed-on: https://go-review.googlesource.com/c/go/+/342474
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>