add basic cuda support for float8 dtypes (#105807)
Summary:
Ensures that creating tensors, copying, filling with zeroes, checking for nan works on cuda for the `float8` dtypes. This should be enough for float8 emulation on cuda.
Note that I skipped the mul test - it's less trivial to add (need a new c++ macro), and there is no use case for it. We can follow up on that in the future.
Test Plan:
```
python test/test_quantization.py TestFloat8Dtype
```
Reviewers:
Subscribers:
Tasks:
Tags:
Fixes #ISSUE_NUMBER
Pull Request resolved: https://github.com/pytorch/pytorch/pull/105807
Approved by: https://github.com/ezyang, https://github.com/jerryzh168, https://github.com/albanD
