Support generalized tear-off

[mkustermann]

This

class A { 
  foo() => 1;
}

main() {
  var o = new A();
  print(o#foo);
}

gets translated to

  class A extends core::Object {
    constructor •() → void
      : super core::Object::•()
      ;     
    method foo() → dynamic
      return 1;
  }
  static method main() → dynamic {
    dynamic o = new test::A::•();
    core::print(o);
    #foo; 
  }

[asgerf]

Generalized tear-offs are not supported yet.