[MPS] Reduce ops multi axes support (#91734)
Currently, most of the reduction ops are flattening the input tensor to 1D to perform the operation.
This change removes the flattening of the tensors / the unranked placeholders and adds support for multi axes in all the reduction ops.
- Fixes reduction ops with correctness and shape issues.
- Fixes masked.argmax / masked.argmin. In case of passing inf to argmax / argmin, MPS will return nan as index for these numbers. Casting this nan to Long will make it -1. This change avoids negative values by clamping them to 0 (matching CPU results).
TestConsistency issues fixed:
```
std
var
amax
amin
sum
prod
mean
count_nonzero
masked.amax
masked.amin
masked.mean
masked.prod
masked.std
masked.sum
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/91734
Approved by: https://github.com/kulinseth
