Implement Stencil Then Cover Path Rendering

[lamarrr]

We need to render 2D Concave Polygons with winding rules, similar to SVGs for complex UI.
Stencil then cover is the fastest general-purpose technique that doesn't require CPU-side triangulation and curvature/intersection analysis like (constrained) Delaunay Triangulation which from our previous undocumented experiments took a quite significant and unacceptable amount of frame time.

Reference: flutter/engine#51219