[inductor][fx passes] batch tanh in pre grad (#107881)
Summary:
Daohang report this pattern in f469463749
{F1074472207}
{F1074473348}
Hence, we can fuse the tanh after same split.
Typically the pattern looks like split->getitem0,...n-> tanh(geitem 0,..., n). Hence, we search for parent node of tahn nodes and the node should be getitem(parent, index). If tanh is after same split node, parent nodes of getitem nodes should be same.
Test Plan:
```
[jackiexu0313@devgpu005.cln5 ~/fbsource/fbcode (c78736187)]$ buck test mode/dev-nosan //caffe2/test/inductor:group_batch_fusion
File changed: fbcode//caffe2/test/inductor/test_group_batch_fusion.py
Buck UI: https://www.internalfb.com/buck2/df87affc-d294-4663-a50d-ebb71b98070d
Test UI: https://www.internalfb.com/intern/testinfra/testrun/9570149208311124
Network: Up: 0B Down: 0B
Jobs completed: 16. Time elapsed: 1:19.9s.
Tests finished: Pass 6. Fail 0. Fatal 0. Skip 0. Build failure 0
```
Differential Revision: D48581140
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107881
Approved by: https://github.com/yanboliang
