[mlir][python] Handle dashes in op name

The python generated code for 
```
def StableHLO_CrossReplicaSumOp : StableHLO_Op<"cross-replica-sum",
```

fails because the python code 

`def cross-replica-sum...` is generated, which is not a valid python name.

https://github.com/openxla/stablehlo/blob/main/stablehlo/dialect/StablehloOps.td#L2109