Extend Move operation to work between Arrays and Objects

[hackerwins]

The move operation still works only on the elements of an Array. It would be nice to expand this so that it can be moved between Objects and Arrays.

https://github.com/yorkie-team/yorkie/issues/43#issuecomment-612295610

We have an example of Kanban board on the demo page, and by completing this task we can show an example of moving cards between boards.

https://yorkie.dev/demo

[jeemyeong]

To do this, I think refactoring move operation to support both ParentCreatedAt and PrevParentCreatedAt is one of solutions. How do you think? If it is correct, I will try it (including yorkie-js-sdk)

[hackerwins]

@jeemyeong

That's right. Since the target element needs to be moved between different parent elements, we need to pass PrevParentCreatedAt which is the previous parent's position and ParentCreatedAt which is the current parent's position to MoveOperation.