Allow registering an operator schema without a kernel (#18551)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/18551
This is helpful for defining a set of operators as an interface but not adding concrete kernels just yet.
The registration logic will ensure that any other libraries that add kernels for these schemas exactly match the schema defined here.
Reviewed By: dzhulgakov
Differential Revision: D14660208
fbshipit-source-id: 7adb5a4876cff5a0ad21d92d8c450cb889f00cc3
