Initial step to transition the Valhalla JVM from the LW1 model to the LW2 model includes:
  - adding back support for Q-signatures
  - removing support for the ValueTypes attribute (value types are now
    discovered by recognizing Q-signatures in field descriptors and
    method signatures)
  - removing of value types consistency checks (not needed anymore)
  - removing support for the ACC_FLATTENABLE access flag *in class files*,
    flattenable fields are now identified from their Q-signature, but
    ACC_FLATTENABLE is still used in the JVM as an internal access flag
  - updating tests to use the new .box and .val syntax in Java instead of the
    __Flattenable and __NotFlattened keywords.