aspect default productions with collection attributes

It'd be useful to specify a base equation for a collection attribute in a aspect default production, for example:

```silver
aspect default production
top::Expr ::=
{
  top.constraints := case top.inhTy of
  | just(ty) -> [constraintEq(top.synTy, ty)]
  | nothing() -> []
  end;
}
```

to ensure that checked and inferred types are the same when bidirectional typing is used.