Refactor creation of CodeGenerator and management of known data_types and functions.

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.

crates/aiken-lang/src/gen_uplc/builder.rs

@@ -293,7 +293,7 @@ pub fn get_generic_id_and_type(tipo: &Type, param: &Type) -> Vec<(u64, Rc<Type>)
 }
 
 pub fn lookup_data_type_by_tipo(
-    data_types: &IndexMap<DataTypeKey, &TypedDataType>,
+    data_types: &IndexMap<&DataTypeKey, &TypedDataType>,
     tipo: &Type,
 ) -> Option<DataType<Rc<Type>>> {
     match tipo {
@@ -346,7 +346,7 @@ pub fn get_arg_type_name(tipo: &Type) -> String {
 
 pub fn convert_opaque_type(
     t: &Rc<Type>,
-    data_types: &IndexMap<DataTypeKey, &TypedDataType>,
+    data_types: &IndexMap<&DataTypeKey, &TypedDataType>,
     deep: bool,
 ) -> Rc<Type> {
     if check_replaceable_opaque_type(t, data_types) && matches!(t.as_ref(), Type::App { .. }) {
@@ -426,7 +426,7 @@ pub fn convert_opaque_type(
 
 pub fn check_replaceable_opaque_type(
     t: &Type,
-    data_types: &IndexMap<DataTypeKey, &TypedDataType>,
+    data_types: &IndexMap<&DataTypeKey, &TypedDataType>,
 ) -> bool {
     let data_type = lookup_data_type_by_tipo(data_types, t);
 
@@ -622,7 +622,7 @@ pub fn monomorphize(air_tree: &mut AirTree, mono_types: &IndexMap<u64, Rc<Type>>
 
 pub fn erase_opaque_type_operations(
     air_tree: &mut AirTree,
-    data_types: &IndexMap<DataTypeKey, &TypedDataType>,
+    data_types: &IndexMap<&DataTypeKey, &TypedDataType>,
 ) {
     if let AirTree::Constr { tipo, args, .. } = air_tree {
         if check_replaceable_opaque_type(tipo, data_types) {
@@ -903,7 +903,7 @@ pub fn modify_cyclic_calls(
 
 pub fn pattern_has_conditions(
     pattern: &TypedPattern,
-    data_types: &IndexMap<DataTypeKey, &TypedDataType>,
+    data_types: &IndexMap<&DataTypeKey, &TypedDataType>,
 ) -> bool {
     match pattern {
         Pattern::List { .. } | Pattern::Int { .. } => true,
@@ -929,7 +929,7 @@ pub fn pattern_has_conditions(
 // TODO: write some tests
 pub fn rearrange_list_clauses(
     clauses: Vec<TypedClause>,
-    data_types: &IndexMap<DataTypeKey, &TypedDataType>,
+    data_types: &IndexMap<&DataTypeKey, &TypedDataType>,
 ) -> Vec<TypedClause> {
     let mut sorted_clauses = clauses;
 
@@ -1943,7 +1943,7 @@ pub fn extract_constant(term: &Term<Name>) -> Option<Rc<UplcConstant>> {
 pub fn get_src_code_by_span(
     module_name: &str,
     span: &Span,
-    module_src: &IndexMap<String, (String, LineNumbers)>,
+    module_src: &IndexMap<&str, &(String, LineNumbers)>,
 ) -> String {
     let (src, _) = module_src
         .get(module_name)
@@ -1957,7 +1957,7 @@ pub fn get_src_code_by_span(
 pub fn get_line_columns_by_span(
     module_name: &str,
     span: &Span,
-    module_src: &IndexMap<String, (String, LineNumbers)>,
+    module_src: &IndexMap<&str, &(String, LineNumbers)>,
 ) -> LineColumn {
     let (_, lines) = module_src
         .get(module_name)