When a fully instantiated generic method is exported, be sure to also
export the types in its signature.
Fixes#52279.
Change-Id: Icc6bca05b01f914cf67faaf1bf184eaa5484f521
Reviewed-on: https://go-review.googlesource.com/c/go/+/405118
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
