Rename generic class params

[soutaro]

Opening generic classes/modules with different parameter names caused a problem that the parameters will be left after a type application. Renaming the type parameters of methods/instance variables solves the problem.

class Foo[A]
  def get: () -> A
end

class Foo[B]        # Use different parameter name.
  def set: (B) -> B
end

# What is the type of Foo[Integer]#set ???