Improve Codegen for `@bind.onready`

At the moment [`this.get_node` ](https://github.com/godotjs/GodotJS/blob/main/scripts/jsb.editor/src/jsb.editor.codegen.ts#L493) can be typed with with generated `SceneNode[XXX]`. 

It would be great if [`onready` ](https://github.com/godotjs/GodotJS/blob/main/scripts/jsb.editor/src/jsb.editor.codegen.ts#L1858) has this feature as well