Added new test typeparam/factimp.go and changed a bunch of other tests
to test exporting more generic functions and types.
Change-Id: I573d75431cc92482f8f908695cfbc8e84dbb36d2
Reviewed-on: https://go-review.googlesource.com/c/go/+/321749
Trust: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
