shiny/iconvg: make HighResolutionCoordinates optional.

On the full Material Design icon set, the 950 or so icons take up around
40% more bytes (172K vs 123K) at high resolution.

Change-Id: I6bd59c3aa75f7fc251c4283a0b244c656f1f9b86
Reviewed-on: https://go-review.googlesource.com/31111
Reviewed-by: David Crawshaw <crawshaw@golang.org>
16 files changed