Tracking issue: support change detection for delete entities & components

For the [hierarchy implementation](https://github.com/AThilenius/legion_transform/tree/master/src) I need a way to detect both deleted entities and components (I don't think I need to disambiguate however, just when any `Parent` or entity that had a `Parent` is deleted).

The ideal case would be to have a separate `deleted` filter that would also give me that last set Component value. I could see this being problematic in terms of leaking memory however.

Tagging @jaynus here too.