[release-branch.go1.18] cmd/compile: set correct package for vars/params/results...

[release-branch.go1.18] cmd/compile: set correct package for vars/params/results from nested instantiation

Fixes #52606

Change-Id: Ib5b2cdbdbce1d516aa10a0df349449b756f2f404
Reviewed-on: https://go-review.googlesource.com/c/go/+/398474
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-on: https://go-review.googlesource.com/c/go/+/403174