[MPS][BE] Code cleanup (#88529)
Various code cleanup in MPS operations:
- Per @kulinseth suggestion move `mpsSupportsCumsum` to `MPSDevice.h` and rename it to
`is_macos_13_or_newer()`
- Move Ventura MPSGraph new operators to `MPSGraphVenturaOps.h` header
- Use `LookupAs` and `CreateCachedGraphAs` to make code more compact
- Formatting
Pull Request resolved: https://github.com/pytorch/pytorch/pull/88529
Approved by: https://github.com/kulinseth
