Prerequisites for CSPRNG (#36631)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36631
Summary of changes
1. Moved random transformation functions to DistributionHelper.h (`uniform_int_from_to_distribution`, `uniform_int_full_range_distribution`, `uniform_int_distribution`) to avoid code duplication between default CPU, CUDA rngs and custom rng extensions
2. Made GeneratorImpl fields protected instead of private
3. Introduced `TORCH_CHECK_IF_NOT_ON_CUDA` that does the same as `TORCH_CHECK` if it is not CUDA/ROCm device
4. To test multiple rng extensions I had to move ops registration to the method `registerOps()`, expose it to python and call it `def setUp(self)`
Test Plan: Imported from OSS
Differential Revision: D21229202
Pulled By: pbelevich
fbshipit-source-id: 6aa3280f2fc3324cf3e748388b5087e3a1e49f23
