deprecate Package; maybe even deprecate DelegateModel etc.

I've always felt that DelegateModel mixes up the model and view, which might be considered an anti-pattern, so I have never had a real use case for it. (Despite that some examples do)

ObjectModel might not be a great pattern to use either (and I also don't normally use it), but maybe it's easier to justify because it's just a compact way of populating stuff into an item view without using a model at all.

But it seems to me that Package is really obscure: I wasn't aware of its existence until yesterday. Having the name available for something else is probably much more valuable than this class is.

I'm pretty sure we should get rid of at least some of this stuff to simplify qtdeclarative and reduce the maintenance burden in Qt 6. So we should make up our minds which ones to get rid of, so we can start deprecating them soon.