Upstream intervals (#870)

Major features:

- Added Interval type, as well as PrimOps asInterval, clip, wrap, and sqz.
- Changed PrimOp names: bpset -> setp, bpshl -> incp, bpshr -> decp
- Refactored width/bound inferencer into a separate constraint solver
- Added transforms to infer, trim, and remove interval bounds
- Tests for said features

Plan to be released with 1.3