Remove absent trick from create CaseTypes / SatisfiedTypes functions

Now that the functions are purely internal, given that we only use them
with Absent=Null, it was simply unnecessary.
Trim some documentation whitespace
Add typeParameters_internal function
Add create InterfaceDefinition function
Internalize create parameters function
Add create ClassDefinition function
Add test for create InterfaceDefinition function
Add test for create ClassDefinition function