go/types, types2: use GOEXPERIMENT to enable alias type parameters
For #46477.
Change-Id: Ia3558f9d2bf43fdd9e3618bd9f800d268e13b367
Reviewed-on: https://go-review.googlesource.com/c/go/+/586956 Reviewed-by: Carlos Amedee <carlos@golang.org> Reviewed-by: Robert Findley <rfindley@google.com> Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Robert Griesemer <gri@google.com>