Make shape matching work for any shaped type.

    The current implementation makes some assumptions about what can be a shaped type, which aren't really necessary. It also has strange behavior for types that aren't in the limited set it handles (e.g. dialect-defined types)

    Updated the comment to match the implementation.

    This is partially motivated by the desire to make MemRef a subclass of ShapedType

--

PiperOrigin-RevId: 248859674