[MPS] Fix gelu forward and backward ops (#94529)
Forward pass:
```
fix gelu_out_mps key
add calculation for gelu with tanh
remove gelu from blocklist
```
Backward pass:
```
fix gelu_backward_out_mps key
uniform format
add caculation for tanh approximate backward pass
unblock grad test from blocklist
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/94529
Approved by: https://github.com/razarmehr, https://github.com/kulinseth
