Fixes the simplifying assumption that shadow casters were always
rectangular.
Java side APIs + plumbing to pass down correct shapes still need to be added.
Change-Id: Ic4fee90af15679951a44bb5cc6ae454b98c4c194
Basically we compute the shadow as a strip of triangles, whose alpha value
is the strength of the shadow.
We use the normal to extend the geometry.
And we use static function and try to avoid new/malloc in the computation.
Change-Id: I382286f1cad351bd5ff983f76f446c075819dcaf
