Implement AnalyticAA for convex shapes.

Implement AnalyticAA for convex shapes.

Design doc: go/analyticAA

A performance test can be found here: https://docs.google.com/a/google.com/spreadsheets/d/1n9LSjFzrQzx0hovFddWey0GSMXNRjl1oFuSypMlHWZk/edit?usp=sharing

Our best case is filling big triangles, which according to our experiment has ~2.9x speedup. Our worst case is filling small ovals/circles, which has a ~1.06x slowdown.

To see how our new algorithm changes the DM images, see: https://x20web.corp.google.com/~liyuqian/dmdiff/index.html
The most significant changes are in convexpaths and analytic_antialias_convex

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2221103002

Review-Url: https://codereview.chromium.org/2221103002