[DispatchCreation] Fuse packed contractions with epilogues and unpack (#24967)

Packed contractions lose their fused epilogues when they arrive at
dispatch formation as mmt4d or a data-tiled convolution. The result
unpack can also become a separate dispatch.

Add opt-in fusion (`fuse-mmt4d`, `fuse-data-tiled-convolution`) of
layout-preserving elementwise consumers and the result unpack. Notes for
review:

- Epilogues must read the contraction result and write their own result
through identity maps. Epilogues that update the result through their
init operand are not matched.
- Only the unpack layouts that data-tiling materialization produces are
matched. For mmt4d that is the row-major form and the narrow-N
transposed form. For convolutions it is NHWC, NCHW and batchless HWC;
batchless CHW is not matched.
- The result unpack is the last op of the group, so a consumer of a
claimed unpack gets its own dispatch instead of fusing with the unpack.
- An unpack that its root does not claim becomes a root at its own
position in program order, as without the options, so it fuses with its
own consumers as before.
- A group holds pack-like ops (`linalg.pack`, `set_encoding`) or the
result unpack, but not both, whichever joins first. A unit-batch
collapse only joins together with the unpack that consumes it, so a
group never ends in the collapse.
- The matchers hardcode the CPU layouts; a TODO describes moving the
layout decision into its own component that dispatch formation queries.

No pipeline enables the options until #24969.

This is one of five PRs adding an experimental CPU path that
materializes data-tiling layouts before dispatch creation, so that
`linalg.mmt4d` and data-tiled convolutions fuse with their elementwise
epilogues and result unpacks.


Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>