internal/number: rename Format to Pattern Format is too overloaded and consists of more than a pattern. Change-Id: I92c08ca82930ef870e619c8fb7ebc6ef1b59bb69 Reviewed-on: https://go-review.googlesource.com/36278 Run-TryBot: Marcel van Lohuizen <mpvl@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Nigel Tao <nigeltao@golang.org>