This also entailed further fleshing out the expression traversal helper
to cover expressions in generate blocks, which could, of course, use
$bits.

- convert default pattern used to fill a vector
- convert Logic in parameter and localparam types
- interface conversion should happen early for type resolution later on
- interface conversion handles renaming of usages of inlined decls

don't prematurely unpack structs with complex types; support for convert patterns that use `default`

- unique0 and priority
- uniqueness on if statements
- preliminary discard-only parsing of assertions
- parameters with alias typenames

allow for stray semicolons in module items; allow for multiple struct field declarations on one line

This should make it much easier to add support for ``, `", macros with
arguments, etc., in the future.