[iOS GPU][BE][3/n] - Rename MetalTensor to MetalTensorImplStorage (#53430)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53430
The definition of Metal tensor is confusing, as we're using it to initialize the MetalTensorImpl. It acts more like a TensorImplStorage.
ghstack-source-id: 123038073
Test Plan:
1. Sandcastle CI
2. Circle CI
3. AIBench/Mobilelab
Reviewed By: SS-JIA
Differential Revision: D26685439
fbshipit-source-id: e0487d0884e4efc3044d627ed0e4af454eca9d67
