[#1037155] API typing: OnChangeCallback param types

[JaylyDev]

export type OnChangeCallback<T extends PropertyBag, Prop extends keyof T & string> = (
    obj: T,
    property: Prop,
    oldValue: object,
    newValue: object,
) => void;

In typings the oldValue and newValue param are referred as object, meanwhile in actual usage in core editor SelectionBehavior class shows both parameters in onChange callback don't return an object, but rather to be it's superset type SelectionCursorMode. It'd be better to have type inference based on the PropertyBag type the item is instantiated with.