This was a mess to say to the least. The mess started when we wanted
to make all definitions in codegen use immutable maps of references --
which was and still is a good idea. Yet, the population of the data
types and functions definitions was done somehow in a separate step,
in a rather ad-hoc manner.
This commit changes that to ensure the project's data_types and
functions are populated while type checking the AST such that we need
not to redo it after.
The code for registering the data type definitions and function
definitions was also duplicated in at least 3 places. It is now a
method of the TypedModule.
Note: this change isn't only just cosmetic, it's also necessary for
the commit that follows which aims at adding tests to the set of
available function definitions, thus allowing to make property tests
callable.
KtorZ