[Feat] Consider adding a new summon actor type

[Pjb518]

The idea here would be to have a special type of actor that can refer to a parent actor to determine its core statistics. In 5e particularly, there are quite a few summon spells and pet class features where the creature takes statistics from the summoner or owner. This typically includes the proficiency bonus of the owner, but attacks sometimes use the owner's spellcasting ability or spell attack mod as well, for example.

I'm not currently assigning this to a milestone, as the idea requires some further discussion and refinement. It may be that the proposal is abandoned.