Running `go tool` with no arguments will now list built in tools
followed by module defined tools.
Running `go tool X` where X matches either the full package path,
or the last segment of the package path, of a defined tool will
build the tool to a known location and immediately execute it.
For golang/go#48429
Change-Id: I02249df8dad12fb74aa244002f82a81af20e732f
Reviewed-on: https://go-review.googlesource.com/c/go/+/534817 Reviewed-by: Michael Matloob <matloob@golang.org> Reviewed-by: Sam Thanawalla <samthanawalla@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>