Enable FP16 sparse regularizer
Summary: Previously there was no regularizer implemented for fp16 sparse features. Add regularizer support here using the Float16SparseNormalize implemented in this stack.
Test Plan:
buck test //caffe2/caffe2/python:regularizer_test
In f248648705, we can see there is the operator `Float16SparseNormalize`.
{F356635445}
Reviewed By: bigrabithong
Differential Revision: D24042567
fbshipit-source-id: 5e0065f8c10b8748daffa8a54a6bf8f461460b18
