Automatically generate attributes and methods for custom backends. (#98066)
Fixes #ISSUE_NUMBER
#97593
A new extension mechanism has been added.
When the user registers a new backend, the corresponding methods and attributes can be automatically generated.
Do this code.
`torch.utils.rename_privateuse1_backend('foo')`
`torch.utils.generate_for_privateuse1_backend()`
Then, get the following methods and attributes.
`torch.Tensor.is_foo`
`torch.Tensor.foo()`
`torch.nn.Module.foo()`
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98066
Approved by: https://github.com/albanD
