Support reading uv and uv map for ply format if texture_uv exists in ply file (#1100)

Summary:
When the ply format looks as follows:
  ```
comment TextureFile ***.png
element vertex 892
property double x
property double y
property double z
property double nx
property double ny
property double nz
property double texture_u
property double texture_v
```
`MeshPlyFormat` class will read uv from the ply file and read the uv map as commented as TextureFile.

Pull Request resolved: https://github.com/facebookresearch/pytorch3d/pull/1100

Reviewed By: MichaelRamamonjisoa

Differential Revision: D50885176

Pulled By: bottler

fbshipit-source-id: be75b1ec9a17a1ed87dbcf846a9072ea967aec37

tests/data/uvs.ply

@@ -0,0 +1,28 @@
+ply
+format ascii 1.0
+comment made by Greg Turk
+comment this file is a cube
+comment TextureFile test_nd_sphere.png
+element vertex 8
+property float x
+property float y
+property float z
+property float texture_u
+property float texture_v
+element face 6
+property list uchar int vertex_index
+end_header
+0 0 0 0 0
+0 0 1 0.2 0.3
+0 1 1 0.2 0.3
+0 1 0 0.2 0.3
+1 0 0 0.2 0.3
+1 0 1 0.2 0.3
+1 1 1 0.2 0.3
+1 1 0 0.4 0.5
+4 0 1 2 3
+4 7 6 5 4
+4 0 4 5 1
+4 1 5 6 2
+4 2 6 7 3
+4 3 7 4 0

tests/test_io_ply.py

@@ -20,10 +20,11 @@ from pytorch3d.renderer.mesh import TexturesVertex
 from pytorch3d.structures import Meshes, Pointclouds
 from pytorch3d.utils import torus
 
-from .common_testing import TestCaseMixin
+from .common_testing import get_tests_dir, TestCaseMixin
 
 
 global_path_manager = PathManager()
+DATA_DIR = get_tests_dir() / "data"
 
 
 def _load_ply_raw(stream):
@@ -778,6 +779,19 @@ class TestMeshPlyIO(TestCaseMixin, unittest.TestCase):
                 data["minus_ones"], [-1, 255, -1, 65535, -1, 4294967295]
             )
 
+    def test_load_uvs(self):
+        io = IO()
+        mesh = io.load_mesh(DATA_DIR / "uvs.ply")
+        self.assertEqual(mesh.textures.verts_uvs_padded().shape, (1, 8, 2))
+        self.assertClose(
+            mesh.textures.verts_uvs_padded()[0],
+            torch.tensor([[0, 0]] + [[0.2, 0.3]] * 6 + [[0.4, 0.5]]),
+        )
+        self.assertEqual(
+            mesh.textures.faces_uvs_padded().shape, mesh.faces_padded().shape
+        )
+        self.assertEqual(mesh.textures.maps_padded().shape, (1, 512, 512, 3))
+
     def test_bad_ply_syntax(self):
         """Some syntactically bad ply files."""
         lines = [