[FX Splitter] dump final graph and print operator stats via to_glow API
Summary:
- dump final graph in glow
- print operator stats via to_glow API
- 1) node stats for final glow graph
- 2) operator stats in TorchGlowBackend for torch::jit::graph to lower
Reviewed By: khabinov
Differential Revision: D28444501
fbshipit-source-id: 743755c320071edc4c045ad004adeb16b4a9c323
