Actually access the nested property

[jrentlez]

Consider the following example:

valuetype WholeNumbers {
  property inner oftype integer;
  constraint isPositive: inner >= 0;
}
valuetype NaturalNumbers {
  property outer oftype WholeNumbers;
  constraint isNonNull: outer.inner != 0;
}

When evaluating outer.inner, we just fetch the value for outer, which is already an integer, and ignore .inner. This is correct for now, because referencing value types with multiple properties is forbidden. Once this is no longer true, we need to remember to change this.

(See the getValueForNestedAccess() function for the relevant code snippet.)