[iOS GPU] Support element-wise broadcasting for binary ops in shaders (#53949)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53949
As title says
ghstack-source-id: 123849745
Test Plan:
`buck test pp-mac`
```
2021-03-11 18:25:07.922375-0800 PyTorchPlayground[8324:5122672] [bool test_add()],[1 180 12 12 ],[SUCCEED]
2021-03-11 18:25:07.960812-0800 PyTorchPlayground[8324:5122672] [bool test_add_broadcast()],[2 17 58 67 ],[SUCCEED]
2021-03-11 18:25:07.978399-0800 PyTorchPlayground[8324:5122672] [bool test_add_broadcast2()],[2 17 1 67 ],[SUCCEED]
2021-03-11 18:25:08.021570-0800 PyTorchPlayground[8324:5122672] [bool test_sub()],[5 3 167 222 ],[SUCCEED]
2021-03-11 18:25:08.034218-0800 PyTorchPlayground[8324:5122672] [bool test_sub_broadcast()],[1 3 1 1 ],[SUCCEED]
2021-03-11 18:25:08.069419-0800 PyTorchPlayground[8324:5122672] [bool test_sub_broadcast2()],[3 3 192 192 ],[SUCCEED]
2021-03-11 18:25:08.112967-0800 PyTorchPlayground[8324:5122672] [bool test_mul()],[2 7 262 119 ],[SUCCEED]
2021-03-11 18:25:08.136691-0800 PyTorchPlayground[8324:5122672] [bool test_mul_broadcast()],[4 3 192 192 ],[SUCCEED]
2021-03-11 18:25:08.148920-0800 PyTorchPlayground[8324:5122672] [bool test_mul_broadcast2()],[1 3 192 192 ],[SUCCEED]
```
Reviewed By: SS-JIA
Differential Revision: D27000487
fbshipit-source-id: f86fca5ac1960ca0a56636da17ae05020c1a4138
