Apply isl.BasicMap to loop domain

So that we can do things like this:

https://relate.cs.illinois.edu/course/cs598apk-f18/f/demos/upload/poly/Diamond%20tiling.html

This would replace/generalize `split_iname`. The idea is to allow the user to input the tile mapping (the second `m` in the above notebook). `split_iname` could then trivially be built on top of this. Asserting `m.is_bijective()` would be an easy sniff test. This would also replace the `affine_map` transformation. It's also trivially compatible with the new dependency system.

cc @jdsteve2 @mattwala