[mlir][x86] Lower Int8 vector.contract to AVX2/AVX10 dp (online packing) (#189386)
A transform pass to lower flat layout `int8` packed type
`vector.contract` operation to:
1. `x86.avx10.int8.dp` - for vector length of `16`, and
2. `x86.avx.int8.dp` - for vector length of `8` via online packing.