types2, go/types: fix instantiation of named type with generic alias
The typechecker is assuming that alias instances cannot be reached from
a named type. However, when type parameters on aliases are permited, it
can happen.
This CL changes the typechecker to propagate the correct named instance
is being expanded.
Updates #46477
Fixes #68580
Change-Id: Id0879021f4640c0fefe277701d5096c649413811
Reviewed-on: https://go-review.googlesource.com/c/go/+/601115
Auto-Submit: Robert Griesemer <gri@google.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>