- substitute enum item values directly into usage sites rather than
  creating synthetic localparams
- substitution handles shadowing of expressions in enum item values
- disconnected scopes can reference conflicting enum items

Disabling the package item injection routine used in the enum conversion
when there were no items to inject exposed cases where conversions would
generate duplicate declarations. The hierarchical constant and param
type conversions were trivially affected. The package conversion could
inject class items within a generate region and then re-inject them
outside of that generate region. The package conversions now uses an
upgraded generate region flattening utility to ensure injected class
items are seen. This also includes coverage for a conflict which
occurred even without the enum conversion change.

- full import and export support
- simplify AST representation of import and export
- allow package-scoped identifiers invoked as subroutines
- use scoped name resolution for identifiers in packages
- merge package item nesting conversion into package conversion
- fix handling of colliding enum items in separate modules
- fix visiting enum item exprs in types

- 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

- single bit localparams retain explicit range
- fix $bits on unsized literals
- use Implicit over Maybe for underlying type

- explicit enum casts in source are converted to size casts
- conversion for basic pattern array literals of unsized numbers
- unsized number array literals preserve signing
- more aggressive ternary simplification

- also adds $clog2 localparam substitution to Simplify

- NestTF refactored to cover all package items
- fixed issue where type traverse skipped typedefs