Also make the STB version policy filer instance specific, rather than a
flyweight with a single instance per version. This is neater as it reduces
the amount of parameter passing, and also means that the classes are
eligible for removal when deploying an image.

If a class defines a class constant that includes subclasses, then the
class definition message will fail to compile unless the classes are
predeclared.

Fix the fact that the predeclaration mechanism is broken in D8, and ensure
that it is tested by the PackageTests.