go/printer: report allocs and set bytes

go/printer: report allocs and set bytes

We now get more than just time/op.

	name      time/op
	Print-16    6.29ms ± 3%

	name      speed
	Print-16  8.25MB/s ± 3%

	name      alloc/op
	Print-16     483kB ± 0%

	name      allocs/op
	Print-16     17.8k ± 0%

Change-Id: I6b5e9a30a826ff8603724bd5983e6b7f5ec12708
Reviewed-on: https://go-review.googlesource.com/c/go/+/412554
Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Ian Lance Taylor <iant@google.com>