[FBGEMM] Open sourcing fbgemm_fp16 ops (#36212)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/36212
Pull Request resolved: https://github.com/pytorch/FBGEMM/pull/342
So that we can let vendor use this as a reference for fp16 emulated ops.
Will modify the dependent TARGETS and CMakefiles.
Test Plan:
```
buck test deeplearning/fbgemm:
```
Reviewed By: hyuen
Differential Revision: D20911460
fbshipit-source-id: bb8a43e13591f295727fe1ecc74eca4ca85ab5b8
