`Resource`-like scripts

[makspll]

I.e. scripts which do get attached to entities, but simply always get executed on each callback regardless of entity.

Should be easier to add, perhaps with a command, AddStaticScript which will add the script ID to a collection of scripts to be considered at each event handler

[Joakker]

Here's how I'd do it

/// Create a new resource that holds the static scripts' ids
#[derive(Resource, Default, Deref, DerefMut)]
pub struct StaticScripts(Vec<ScriptId>);

/// The base ScriptingPlugin adds the resource
/// That way we don't need to repeat it for every language we want to impl
/// scripting for
impl Plugin for ScriptingPlugin {
    fn build(&self, app: &mut App) {
        app
            .init_resource::<StaticScripts>()
            ...
            ;
    }
}

/// A utility trait
pub trait AddStaticScript {
    fn add_static_script(&mut self, path: &str);
}

impl AddStaticScript for World {
    fn add_static_script(&mut self, path: &str) {
        self.resource_scope(|_, mut static: Mut<StaticScripts>| static.push(path.into())) ;
    }
}

/// Same for App, which fetches the world and calls the above method, and make a custom command that does the same in the apply method