[PyTorch][caffe2] Add CAFFE2_{DECLARE,DEFINE}_KNOWN_TYPE (#83707)
It looks like we aren't getting inlining for the defined `_typeMetaData` functions from CAFFE_KNOWN_TYPE and there's some cost associated with that. I added new macros that fix this problem; I will migrate to them in a follow-up after I get buy-in from reviewers.
Differential Revision: [D36883685](https://our.internmc.facebook.com/intern/diff/D36883685/)
**NOTE FOR REVIEWERS**: This PR has internal Facebook specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D36883685/)!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/83707
Approved by: https://github.com/ezyang
