add bfloat16 conversion method in type stub (__init__.pyi) (#33747)
Summary:
Resolve https://github.com/pytorch/pytorch/issues/33699
`torch/__init__.pyi` will be generated like
```python
# TODO: One downside of doing it this way, is direct use of
# torch.tensor.Tensor doesn't get type annotations. Nobody
# should really do that, so maybe this is not so bad.
class Tensor:
requires_grad: _bool = ...
grad: Optional[Tensor] = ...
# some methods here...
overload
def bernoulli_(self, p: _float=0.5, *, generator: Generator=None) -> Tensor: ...
def bfloat16(self) -> Tensor: ...
def bincount(self, weights: Optional[Tensor]=None, minlength: _int=0) -> Tensor: ...
# some methods here...
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33747
Differential Revision: D20090316
Pulled By: ngimel
fbshipit-source-id: b9ce4c0d4ef720c94ccac0a0342a012e8cf3af0c
