[inductor] Reduce device context manager overhead (#91045)
This adds `torch.cuda._DeviceGuard` which is a stripped down version of
`torch.cuda.device` with lower overhead. To do this, it only accepts `int` as
the device so we don't need to call `_get_device_index` and is implemented
with a new C++ helper `torch._C._cuda_exchangeDevice` that allows
`_DeviceGuard.__enter__` to be just a single function call. On my machine,
I see a drop from 3.8us of overhead to 0.94 us with this simple benchmark:
```python
def set_device():
with torch.cuda.device(0):
pass
%timeit set_device()
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/91045
Approved by: https://github.com/ngimel, https://github.com/anijain2305
