Report when notypes are generated for method definitions

[wiwa]

Instead of leaving notypes in the outlines and failing upon Scalac using those notypes, we can instead error out or warn the user of any notypes when they are generated, perhaps with a helpful error message telling them where to ascribe the type.

Some caution is necessary: since notypes only result in an error when Scalac tries to use them, the act of simply generating a notype would not necessarily result in an unsupported program.