go/types, types2: operand.AssignableTo must consider Alias types

go/types, types2: operand.AssignableTo must consider Alias types

Fixes regression from Go 1.22.

For #67547.

Change-Id: Id0d07d6b24e1eab6ed1c7476d9d9b82d28aee80a
Reviewed-on: https://go-review.googlesource.com/c/go/+/587161
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>