internal/number: factor out logic to compute visible digits

This is needed for the plural computation.
Leading zeros are not needed for this computation.

Change-Id: Ib82e9270b5df3e7314d79215bfb7c6c847bd5909
Reviewed-on: https://go-review.googlesource.com/47591
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
2 files changed