Amending an undefined property via `super` member access always amends `new Dynamic {}`

[HT154]

It's weird that this does not produce an error:

abstract class Bird {
  name: String
}

class Parrot extends Bird {
  name = "Polly"
  lifespan = (super.lifespan) { // Bird does not define a property lifespan
    min = 5
    max = 20
  }
}

mybird = new Parrot {}

Adding a trace() around super.lifespan indicates this expression has value new Dynamic {}.

This behavior makes sense in dynamic context where the parent may not define properties the child needs to amend, eg.

foo { // this is in module definition context
  bar { // this is in Dynamic object body context
    baz = true
  }
}
// which is syntax sugar for:
foo = (super.foo) {
  bar = (super.bar) {
    baz = true
  }
}

But in a typed context where the full set of properties of the parent is known, attempting to access an unknown property should result in an error like this:

Cannot find property `lifespan` in object of type `bird#Bird`.

[bioball]

We definitely want to improve this, but it's not as simple as "lookup on a Typed should fail". A module is also a Typed, and this syntax should still work:

foo {
  res = 1
}