Implement ScrollBarView

[bjorn-einar-bjartnes-4ss]

Description

The scrollbarview is not implemented
https://github.com/DieselMeister/Terminal.Gui.Elmish/blob/4d44c8c8e23e6a9a410a8a777c441474a8b5ad35/src/Terminal.Gui.Elmish/Views.fs#L63

Related information

Do you know where it stopped? I would like to give it a try to implement it, as I need it, but given that it is just commented out I am worried it might be hard to do? I was just wondering what stopped it, if it was a major thing then I guess I should not pick it up as a first task...

[bjorn-einar-bjartnes-4ss]

(I notice that text in a textview does have scrolling, so it seems this is mostly about giving some indicator to the ScrollBarView about the size of its children, I found this gui-cs/Terminal.Gui@61e87e8 which seems related)

I was mostly wondering if you think this is something that would require significant changes, as it seems it does need to ask the children for its size somehow, or if it is something that can be implemented without refactoring other parts of the codebase with regards to communicating with the children views somehow)