Add utility to extract strides from layout map in MemRefType.

Add utility to extract strides from layout map in MemRefType.

The RFC for unifying Linalg and Affine compilation passes into an end-to-end flow discusses the notion of a strided MemRef (https://groups.google.com/a/tensorflow.org/forum/#!topic/mlir/MaL8m2nXuio).

This CL adds helper functions to extract strides from the layout map which in turn will allow converting between a strided form of the type and a layout map.

For now strides are only computed on a single affine map with a single result (i.e. the closed subset of linearization maps that are compatible with striding semantics). This restriction will be reevaluated / lifted in the future based on concrete use cases.

PiperOrigin-RevId: 270284686