cmd: relocate cmd/go/internal/robustio to cmd/internal/robustio
Relocate cmd/go's internal/robustio package up a level into
cmd/internal/robustio, so that it can be used by other cmd/internal
packages. No change in functionality. This change is intended to be in
support of making the cmd/go script test framework available to other
commands in addition to just the Go command.
Updates #68606.
Change-Id: Ic8421ef59d9b7d79a50c3679d180cfa2546c4cd3
Reviewed-on: https://go-review.googlesource.com/c/go/+/601356
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Michael Matloob <matloob@golang.org>