Create J9ModuleIterator and J9PackageIterator

[Ailloviee]

Related: https://github.com/eclipse/openj9/pull/2192

This is a discussion on whether or not I should make a new J9ModuleIterator and new J9PackageIterator to iterate through all modules & packages in jvm.

The iterator would go through all class loaders and the module/package hash tables in the them. The pattern would look like:

GCClassLoaderIterator iterator = GCClassLoaderIterator.from();
while (iterator.hasNext()) {
    J9ClassLoaderPointer classLoaderPointer = iterator.next();
    HashTable<J9ModulePointer> moduleHashTable = ModuleHashTable
        .fromJ9HashTable(classLoaderPointer.moduleHashTable());
    SlotIterator<J9ModulePointer> slotIterator = moduleHashTable.iterator();
    while (slotIterator.hasNext()) {
        J9ModulePointer modulePtr = slotIterator.next();
    }

Currently the common code pattern appeared three times in https://github.com/eclipse/openj9/pull/2192 (one for Package and two for Module)

[Ailloviee]

fyi @keithc-ca @tajila