Be able to access mut window state from tabviewer

[foduckthetugboat]

I'd like to be able to set a preferred window size when a tab is dragged into its own window

I could iterate all tabs in tree before drawing and try to keep current tab indexes in each tab struct, but it seems error prone.

If there was a way in rect changed to get that info, it could work.

allowed in windows fails because its non mutable

Edit: Tab param in allowed in windows is mutable so I can do what I want that way, but prob not idea