remove sprintf

Most uses of sprintf are
in pathops testing.

Replace them with
SkString::appendf

and replace the remaining
with snprintf

R=scroggo@google.com
BUG=skia:2716
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2391133005

Review-Url: https://codereview.chromium.org/2391133005
12 files changed