[MPS] Fix LSTM backward and forward pass (#95137)
Fixes #91694
Fixes #92615
Several transpositions were missing for backward graph in case of `batch_first=True`. The #91694 is not reproduced with `batch_first=False`.
After fixing transpose issue, I finally thought that now I can use LSTM freely in my project. And then I got horrific results on train. Seems related to #92615.
After that I decided to fix LSTM's backward step completely. I collected all my findings in this thread — seems like I succeeded
Funny enough, backward tests were completely disabled before and were not passing:
```python
@unittest.skipIf(True, "Backward of lstm returns wrong result")
def test_lstm_2(self, device="mps", dtype=torch.float32):
```
UPD: forward pass of multi-layer version also was wrong due to the incorrect `initState, initCell` slices. Tests were passing because states were inited with zeros. *Accidentally* fixed this too
Pull Request resolved: https://github.com/pytorch/pytorch/pull/95137
Approved by: https://github.com/jhavukainen, https://github.com/kulinseth, https://github.com/soulitzer
