[ASObject] Intoduce a simpler interface for calling getters and methods
[EventDispatcher] Call AS getter

The LoaderEvent class from the https://www.greensock.com/loadermax/
library, which is used by many sites, depends on dispatchEvent calling
an overridden AS getter.
[EventDispatcher] Use the new simpler interface for calling a method
[BitmapData] Fix bounds checking in fillRect()