[Snippets] SplitDimensionM unification (#34508)
### Details:
This PR consolidates M-dimension splitting logic into
`MHAParallelWAOptimizer`.
- *Deleted graph-level `SplitDimensionM` pass, which was formerly used
for static shapes,*
- *All the split m dimension related heuristics are moved to the
`MHAParallelWAOptimizer`.*
- *Adapt the snippets pipeline to trigger `MHAParallelWAOptimizer` in
static shape cases.*
### Tickets:
- *CVS-148805*
### AI Assistance:
- *AI assistance used: yes*
- *AI was used to productize the PoC (created some time ago), and debug
the `MHAParallelWAOptimizer` issues related to static shapes pipeline.
The correctness has been checked by CPU plugin functional tests*
---------
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
