Develop a convex path SDF renderer #183960

#183959 requests an SDF renderer for any path, but the realm of convex paths might have a simpler solution that Impeller can add by leveraging existing path transformation utilities such as the path shadow and path stroking code. Even if we don't implement a solution for all paths, a solution for convex paths may cover a large percentage of Flutter rendering and it may also provide a solutions for the basic shape primitives if no computational SDF function exists for them.