Investigate if we can improve the interpretation of generics

[wouterdb]

For references, in to_dsl_type and get_reference_type we have to determine the concrete value of Reference[T]

We can handle the cases

Reference[str]

class TestRef(Reference[str]):
  pass

We can't handle the case

class DaRef[T,S](Reference[S]):
  pass

this is related to ilevkivskyi/typing_inspect#110