Operator generator based on templated selective build. (#43456)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43456
Introduce the template OperatorGenerator, which returns an optional Operator. It's null if the templated bool value is null.
RegisterOperators() is updated to take the optional Operator. A null will not be registered.
With this update the selective operator registration can be done at compile time. Tests are added to show an operator can be registered if it's in a whitelist and it will not be registered if it's not in the whitelist.
Test Plan: Imported from OSS
Reviewed By: ljk53
Differential Revision: D23283563
Pulled By: iseeyuan
fbshipit-source-id: 456e0c72b2f335256be800aeabb797bd83bcf0b3
