Interestingly, this constitutes an implementation of `AsBroadcaster`. It appears Macromedia decided to implement event handling on `MovieClipLoader` in a very similar fashion to `AsBroadcaster`, down to invoking `broadcastMessage` and searching a `_listeners` property for listeners.
*De*implement the free function versions of the above, as well as their `Num` variants, since they don't actually exist as callables. Instead, the ActionScript compiler treats them as preprocessor functions that represent various forms of `ActionGetURL`/`ActionGetURL2`.
This function is part of `Avm1`, rather than a hypothetical `LayerManager`, because we're going to need to eventually construct layers differently for AVM2.
This is a very rough stub out of Stage.width and height to get
basic V-cams to start functioning.
TODO: Implement the different stage scaling modes. We will probably
want to add a "Stage" display object to handle this.
While I don't expect every host object to implement it correctly, this also gets rid of a lot of unnecessary `unwrap` calls that would allow a poorly-written Flash file to kill the interpreter.
Note that host objects that do so will *not* have access to their standard representation from within member functions - you will need to extend the interface to accomodate for them. This is due to long-standing limitations with type IDs and downcasting with types that bear lifetimes - it's entirely an unsafe operation and exposing such a facility to safe Rust is unsound. However, this will at least let us separate out several things from ScriptObject that don't need to be there for the time being.
`Object::function` now returns a pre-allocated function object. You may supply it an explicit prototype to have it linked into the function object (which is why we have to return a cell).
This type explicitly signals if an immediate value is to be returned, if a value is to be returned on the stack, or if no return value is to be generated. Holders of a `ReturnValue` can also use `and_then` to schedule a `StackContinuation` to be executed when and if that value is ready.
`StackContinuations` now yield `ReturnValues` as well, so they have a moderate level of composability. For example, if you need to get a property from an object and push it on the stack, you can return the result of calling `get` directly and the machinery ensures it eventually gets there.