[cpp] Return CallableData instead of T for 'call' member

std/cpp/Callable.hx

@@ -31,8 +31,8 @@ typedef CallableData<T> = T;
 abstract Callable<T>( CallableData<T> )
 {
    inline public function new(inValue:T) this = inValue;
-   public var call(get,never):T;
-   inline function get_call():T return this;
+   public var call(get,never):CallableData<T>;
+   inline function get_call():CallableData<T> return this;
 
    #if cpp
    @:from