Allow Resources & `/variables` utilities in every argument where it makes sense

[GrantGryczan]

Like how execute.run accepts the parameters of MCFunction. It would make checks with predicates that are only ever used once much less verbose.

I am iffy on this suggestion though, because there are a lot of commands that could receive the same treatment but don't (for example, the item command could allow the creation of ItemModifiers via its parameters too), and I'm not confident this is a good design pattern for anything beyond functions. More opinions (or deeper consideration) would be needed.