Add MKLDNN fuser (#51600)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51600
Looking for notes on implementation first, will post more notes on benchmarks and overall thoughts/implementation and solicit more input soon.
Test Plan: Imported from OSS
Reviewed By: navahgar
Differential Revision: D26696702
Pulled By: eellison
fbshipit-source-id: cd612f093fe3859e42fb0b77560ebd1b44fccff7
