[LinalgExt] Add decomposition for vector map_scatter

[Max191]

Adds a decomposition pass for iree_linalg_ext.map_scatter with a vector input and a memref output. The decomposition lowers the op into a series of vector ops to compute the index vector, and a vector.scatter op. This transformation completes the lowering of a vectorized map_scatter op.

The map_scatter op does not implement the AggregatedOpInterface, because the interface uses an OpBuilder to decompose operations, but the decomposition for map_scatter needs a RewriterBase, so it does not work with the current interface.