[XPU][OptRed] Revamp -tritonintelgpu-optimize-reduction-locality (#2800)

Original implementation had two critical issues:

- *Functional*: It did not preserve register order, so it was computing
a different reduction.
- *Performance*: When converting back to the original tensor type, it
did: `reshape(convert_layout(res))`. That means the `reshape` operation
served as an anchor and the suboptimal slice layout was propagated.

This was fixed as follows:

- Keep register order.
- Do `convert_layout(reshape(res))` when converting back to the original
type, thus propagating the more optimal layout.

See implementation for further details.

Signed-off-by: victor-eds <[email protected]>

Author: victor-eds