Get Ref<Component> from a query by entity

[ThomasAlban]

Currently, as far as I know, there's no API for getting a Ref<Component> from a query.get(entity).unwrap() without changing the query to be a Query<Ref<Component>> or having to do Ref::from(query.get_mut(entity)). Would be nice if this was added!

[alice-i-cecile]

We'll want this on Query, QueryState, EntityRef, EntityMut, and probably EntityWorldMut 🙃

Should be quite approachable, but you'll need some bravery exploring the ECS!

[Adamkob12]

I'd like to try if that's ok.

[alice-i-cecile]

Sounds good! Don't hesitate to open a draft PR and then ask for help :)

[alice-i-cecile]

As discussed in #11545, the complexity is too high here relative to the value. Maybe one day with effects.