Rename CPUGenerator to CPUGeneratorImpl and CUDAGenerator to CUDAGeneratorImpl (#36026)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/36026
Differential Revision: D20856458
Pulled By: pbelevich
fbshipit-source-id: 6d105593dca67640d508a4aebf7edf028d52af32
