Avoids using mzlib/pconvert in favor of a few big match
clauses. This lets us cut out a package dependency and
makes the code easier to understand.
This commit also removes the use of mzlib/pconvert
in the debug printer in favor of just using the type
serialization performed in init-envs.rkt.
In addition, a few optimizations for type serialization
were implemented that cut a few percent off of zo sizes.
Note that this commit regresses for zo sizes for modules
that heavily use GUI classes, but that is fixed in a
future commit.
