This reverts commit 51f2d2bb.

- added type class for looking up elements in scoped conversions

- support casts of generate scoped expressions
- support casts to sizes involving genvars

- number literals are parsed rather than stored as strings
- fix array query functions used on non-trivial number literals
- more efficient expression simplification recursion
- expanded constant folding scenarios

- elaborated literals larger than 32 bits are given an explicit size
- constant folding no longer encodes illegal negative numbers

- support ubased unsized bound to ports using injected constants
- explicit context-aware literal sizing for complex expressions
- fix infinite loop case in NestPI conversion
- elaborate size-casts of converted literals