go/types, types2: add Alias.{TypeParams, SetTypeParams, TypeArgs, Origin}

go/types, types2: add Alias.{TypeParams, SetTypeParams, TypeArgs, Origin}

Fixes #67143.

Change-Id: I8bf9c2559f95d3d6a40874454208ae074b68875c
Reviewed-on: https://go-review.googlesource.com/c/go/+/583757
Reviewed-by: Alan Donovan <adonovan@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>