[iOS][GPU] Add Metal/MPSCNN support on iOS (#46112)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46112
### Summary
This PR adds the support of running torchscript models on iOS GPU via Metal (Inference only). The feature is currently in prototype state, API changes are expected. The tutorial and the documents will be added once it goes to beta.
allow-large-files
- Users API
```
auto module = torch::jit::load(model);
module.eval();
at::Tensor input = at::ones({1,3,224,224}, at::ScalarType::Float).metal();
auto output = module.forward({input}).toTensor().cpu();
```
- Supported Models
- Person Segmentation v106 (FB Internal)
- Mobilenetv2
- Supported Operators
- aten::conv2d
- aten::addmm
- aten::add.Tensor
- aten::sub.Tensor
- aten::mul.Tensor
- aten::relu
- aten::hardtanh
- aten::hardtanh_
- aten::sigmoid
- aten::max_pool2d
- aten::adaptive_avg_pool2d
- aten::reshape
- aten::t
- aten::view
- aten::log_softmax.int
- aten::upsample_nearest2d.vec
- Supported Devices
- Apple A9 and above
- iOS 10.2 and above
- CMake scripts
- `IOS_ARCH=arm64 ./scripts/build_ios.sh -DUSE_METAL=ON`
### Test Plan
- Circle CI
ghstack-source-id: 114155638
Test Plan:
1. Sandcastle CI
2. Circle CI
Reviewed By: dreiss
Differential Revision: D23236555
fbshipit-source-id: 98ffc48b837e308bc678c37a9a5fd8ae72d11625
