Enhancement: Rename `init` to `scriptInit` for creating scripted classes

[KoloInDaCrib]

Currently, to init a scripted class, you have to run [ScriptedClass].init([name], [params]);. However, due to the name of this function and due to the fact that Haxe doesn't support having an instance and a static function with the same name, several classes that already have an init function of their own such as FlxSound cannot be made scriptable.

My proposed solution would be to rename the initialization function to scriptInit and to implement some sort of backwards compatibility to PolymodInterpEx. That way, not only is the problem of some classes not being possible to script avoided, but it would also follow the naming convention of other HScriptClassMacro methods (scriptGet, scriptSet, scriptCall).