make sharing code between modules generated by providers efficient

some modules need to be "enriched" before they become truly usable, for example qt.core needs Rules for moc and rcc. while in principle it would be possible to have each provider do that individually, it is better to centralize this somehow: one could

1. share code between the generated modules by making them depend on additional modules which come with the providers
2. share code+data between the providers, but have the generated modules duplicate the enrichments
3. introduce some kind of post-processing which automatically kicks in regardless which provider generated a module. a ModulePatcher Item that is parameterized with a module name and some injection rules could do that

for the first two methods, it would be preferable to be able to specialize generic providers by overriding them in a namespace and implementing some hook. the alternative would be "librarizing" the providers as much as possible and duplicating the remaining implementation for each specialization.
the third method essentially externalizes the "hooking".

the last two methods create self-contained modules, which probably isn't much of an advantage.