[Gradient Compression] Make FP16 compression as a wrapper that can be combined with other communication hooks (#53808)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53808
Create a FP16 wrapper that can combine FP16 gradient compression with any gradient compression algorithm.
Test Plan:
Unit test:
```
buck test mode/dev-nosan caffe2/test/distributed:c10d -- test_fp16_compress_wrapper
```
Performance Test on DDP QPS Benchmark: Check if AllReduce + FP16 Wrapper = FP16 Compression
1) FP16 Compression:
f256897690
2) FP16 Wrapper + AllReduce (after patching D26960986):
f256897289
Reviewed By: SciPioneer
Differential Revision: D26978832
fbshipit-source-id: 0dcd18b050c02f5e9f3cff56344d1f39a04e20c0
