Added distance vector support for CircleGeometryProcessor

This CL's base is the CL that sets up the distance vector field req. exposure: https://codereview.chromium.org/2114993002/

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2190023002

Committed: https://skia.googlesource.com/skia/+/779e1924eaf7c5652dee93e0e8e975bbf5723b37
Review-Url: https://codereview.chromium.org/2190023002
1 file changed