Add loop nest constraints v2 to better loop around nest map

[jdsteve2]

@kaushikcfd I did my best to clean this up and pull out the parts that will be useful to your new linearization stuff. Once your linearization step is incorporating the constraints, I can copy in more of my tests (the ones that make sure linearization follows the constraints). Let me know if anything is unclear.

PS: My code will probably be easiest to understand if you can take advantage of all the vim fold markers, rather than using github's "Files changed" view; pretty much all of my code is self-contained, so there's not much benefit to the side-by-side comparison.

Targets #350.

New PR directly against main