add version of the ecs's write_world method that takes a pre-boxed …

[blunted2night]

This is a simple change to add an alternate API that allow us to post a "pre-boxed" world writer to the ECS's command queue.

[cart]

Seems reasonable, but before merging I'd like to know the use case this enables. I'd prefer to keep the api lean unless this unlocks new scenarios.

[blunted2night]

In my case, I am playing with a keyboard focus system. There is a type erased handler as a property of my keyboard state resource that can generate type erased units of work against the world. I would use it by having an entity, say a text editor, gain focus by setting the handler and having that handler generate a world writer that makes the appropriate changes to what ever entities and components are necessary. Another type of widget would be able to gain focus and handle keyboard input differently without having to share knowledge between components beyond the handler interface.

I think it could be used in additional contexts where runtime polymorphism would allow low frequency work to be easier to express.

[cart]

Cool cool that seems reasonable to me.