CUDA/C++ Rasterizer updates to handle clipped faces

Summary:
- Updated the C++/CUDA mesh rasterization kernels to handle the clipped faces. In particular this required careful handling of the distance calculation for faces which are cut into a quadrilateral by the image plane and then split into two sub triangles i.e. both sub triangles can't be part of the top K faces.
- Updated `rasterize_meshes.py` to use the utils functions to clip the meshes and convert the fragments back to in terms of the unclipped mesh
- Added end to end tests

Reviewed By: jcjohnson

Differential Revision: D26169685

fbshipit-source-id: d64cd0d656109b965f44a35c301b7c81f451cfa0

tests/test_render_meshes.py

@@ -994,6 +994,7 @@ class TestRenderMeshes(TestCaseMixin, unittest.TestCase):
             blur_radius=0.0,
             faces_per_pixel=1,
             cull_backfaces=True,
+            perspective_correct=False,
         )
 
         # Init shader settings