test: add test for findTypeLoop with symbols from other packages

test: add test for findTypeLoop with symbols from other packages

CL 274294 improved findTypeLoop but also fixed a new found bug on master
branch. This Cl adds test cases for this.

Updates #44266

Change-Id: Ie4a07a3487758a1e4ad2f2847dcde975b10d2a77
Reviewed-on: https://go-review.googlesource.com/c/go/+/292889
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>