OwningPtr should impl From<Box<T>> about bevy

[SkiFire13]

Another reason why this should be avoided is that OwningPtr only owns the data, not the allocation, so the proposed conversion would have to leak the allocation.

I would instead suggest using ReflectComponent to insert a reflected value as component.

[MrGVSV]

Note that for dyn Reflect we probably want to only do this via the ReflectFromPtr type data.

The reason for this is because a Box<dyn Reflect> might not actually be a Box<T>.

Specifically, when cloning via Reflect::clone_value, you almost always get back a dynamic type (e.g. Box<DynamicStruct>). It would be unsafe to treat the OwningPtr as one that points to T when it really points to DynamicStruct.

So ideally we expose this API through the ReflectFromPtr type data to help ensure these kinds of operations are done safely.