[inductor][fx passes] batch layernom (#105492)
Summary: Batch layernorm. Fuse independent horizontal layernorm with same size into one.
Test Plan:
# unit test
```
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/buck2/68eb51e1-bdbc-4847-aabf-e50737d8485b
Test UI: https://www.internalfb.com/intern/testinfra/testrun/5066549764442206
Network: Up: 0 B Down: 0 B
Jobs completed: 10. Time elapsed: 1:07.2s.
Tests finished: Pass 3. Fail 0. Fatal 0. Skip 0. Build failure 0
```
Differential Revision: D47447542
Pull Request resolved: https://github.com/pytorch/pytorch/pull/105492
Approved by: https://github.com/jansel, https://github.com/xuzhao9
