This wasn't possible before because there was no support for affine expressions
as maps. Now that this support is available, provide the mechanism for
constructing maps with a layout and inspecting it.
Rework the get method on MemRefType in Python to avoid needing an explicit
memory space or layout map. Remove the get_num_maps, it is too low-level,
using the length of the now-avaiable pseudo-list of layout maps is more
Depends On D94297