Temporarily add modload.State field to the Switcher implementation.
Note that we cannot modify the gover.Switcher interface because doing
so creates an import cycle.
This commit is part of the overall effort to eliminate global
modloader state.
Change-Id: I20dba76328aa3d0df58caff75b174522bf9df9d5
Reviewed-on: https://go-review.googlesource.com/c/go/+/712703
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Michael Matloob <matloob@google.com> Reviewed-by: Michael Matloob <matloob@golang.org>