types2, go/types: use slices.SortFunc

types2, go/types: use slices.SortFunc

Now that we're bootstrapping from a toolchain that has the slices
package.

Updates #64751

Change-Id: I3227e55f87e033dae63a2d1712b7f9373fe49731
Reviewed-on: https://go-review.googlesource.com/c/go/+/610603
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Findley <rfindley@google.com>