[dte] broadcast fastpath implementations for reduce utility functions (2/x) (#62428)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62428
In this diff we add a broadcast fastpath for reduce utility functions. These functions are used by various elementwise ops, whose tests we update to exercise the new functionality.
Test Plan: Added test cases to elementwise ops (which will exercise the new reducer functionality) that will be run by CI. It's worth noting there's still no code (outside of the new test cases) that takes the new code paths added -- the user must explicitly request `allow_broadcast_fastpath=True`, and nothing outside of the added tests currently does so.
Differential Revision: D29938264
fbshipit-source-id: 5d5542bd93afb85fd9f7a4073f766adc07eb3b65
