cmd/go: inject loaderstate into matcher function

cmd/go: inject loaderstate into matcher function

This change alters the matcher function in vendorPkg in order to
retrieve the go version from the current loaderstate.

This commit is part of the overall effort to eliminate global
modloader state.

Change-Id: Iedb12bdfe4ab3c24dbbf161db1f3842014415c59
Reviewed-on: https://go-review.googlesource.com/c/go/+/711117
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Matloob <matloob@golang.org>
Reviewed-by: Michael Matloob <matloob@google.com>