[Codegen] Add pass to absorb swizzle hints into alloc attributes (#24000)

Part 1/3 of enabling XOR swizzle with pipelining (#23919).

**Overall plan:** `SwizzleHintOp` in the SSA chain blocks both
`memref::multiBuffer` and `scf::pipelineForLoop`. The fix absorbs the
hint into an alloc attribute before pipelining, preserves it through
multi-buffering, then re-inserts hints at leaf users afterward.

**This PR:** Adds `AbsorbSwizzleHintToAllocPass`, which moves swizzle
info from `SwizzleHintOp` to an `iree_codegen.swizzle` attribute on the
defining `memref.alloc` and erases the hint op. The pass is not yet
wired into any pipeline.

Assisted-by: Cursor (Claude)

Signed-off-by: Yu-Zhewen <zhewenyu@amd.com>