New dependency and nest constraint semantics development (PR v2)

[jdsteve2]

This branch accumulates changes related to the updates to the loopy dependency and loop-prioritization semantics.

Moved to github from from old gitlab MR.

Next pull request to merge into this branch: Statement instance order and lex order map

Note: A previous PR merging the same branch was created before. This one replaced it after @jdsteve2 could not determine the cause of a merging issue.

Subsumed by #479.