Improve repr for torch.iinfo & torch.finfo (#40488)
Summary:
- fix https://github.com/pytorch/pytorch/issues/39991
- Include directly `min`/`max`/`eps`/`tiny` values in repr of `torch.iinfo` & `torch.finfo` for inspection
- Use `torch.float16` / `torch.int16` instead of uncorrespond names `Half` / `Short`
- The improved repr is shown just like:
```
>>> torch.iinfo(torch.int8)
iinfo(type=torch.int8, max=127, min=-128)
>>> torch.iinfo(torch.int16)
iinfo(type=torch.int16, max=32767, min=-32768)
>>> torch.iinfo(torch.int32)
iinfo(type=torch.int32, max=2.14748e+09, min=-2.14748e+09)
>>> torch.iinfo(torch.int64)
iinfo(type=torch.int64, max=9.22337e+18, min=-9.22337e+18)
>>> torch.finfo(torch.float16)
finfo(type=torch.float16, eps=0.000976563, max=65504, min=-65504, tiny=6.10352e-05)
>>> torch.finfo(torch.float32)
finfo(type=torch.float32, eps=1.19209e-07, max=3.40282e+38, min=-3.40282e+38, tiny=1.17549e-38)
>>> torch.finfo(torch.float64)
finfo(type=torch.float64, eps=2.22045e-16, max=1.79769e+308, min=-1.79769e+308, tiny=2.22507e-308)
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40488
Differential Revision: D22445301
Pulled By: mruberry
fbshipit-source-id: 552af9904c423006084b45d6c4adfb4b5689db54
