Summary:
A tool to track events in graph split, specifically on how nodes being end up in acc or cpu subgraphs.
Usage: use env var to specify a mode and necessary arguments.
FX_NET_ACC_SPLITTER_TRACKER_MODE: Tracker mode.
```
Different modes of the event tracker:
"0": Tracker not enabled (by default)
"1": Tracker enabled but no dumps. Information available by setting breakpoints and visually inspect in pdb.
"2": Tracker enabled and dumps all events to DUMP_PREFIX_all.txt
"3": In addition to events dump, track nodes specified by ENV_FX_NET_ACC_SPLITTER_TRACKER_TRACKED_NODES recusrively and dump to DUMP_PREFIX_nodex.txt
"4:: In addition to events dump, track all nodes with more than 1 event recusrively and dump to DUMP_PREFIX_nodex.txt
```
FX_NET_ACC_SPLITTER_TRACKER_DUMP_PATH: overriding dump path. Leave empty for `~`.
FX_NET_ACC_SPLITTER_TRACKER_TRACKED_NODES: Nodes to track for mode "3".
Test Plan: New unit test
Reviewed By: georgiaphillips
Differential Revision: D79203595
Pull Request resolved: https://github.com/pytorch/pytorch/pull/159795
Approved by: https://github.com/ezyang
