* Refactor windows to not share widget state
* First half of refactoring all the windows
* Refactor the remaining windows, compiles but has issues
* Fix drawing only every second widget
* Remove the need of an terminating widget
* Address WidgetIndex signedness issues; use kWidgetIndexNull more
* Address constexpr issue with Widget content union
* Fix tabs in scenery window
* Fix tabs in object selection window
* Adjust custom widget index for CustomTool events
* Use STR_NONE for default tooltip initialisation
* Adjustment for mingw compiler
* Fix bottom toolbar using the widget declaration not instance
* Remove pointless code in Guest window, handled by SetPage
* Prevent out of bounds crash
* Move scroll widgets initialization to SetPage in Cheats window
* Remove special logic in Options window
* Remove special logic in Park window
* Remove special logic for Player window
* Remove special logic for Research window
* Remove special logic for Ride window
* Remove special logic for Staff window
* Remove special logic for Finances window
* Remove special logic for MapGen window
* Remove special logic for editor objective options window
* Remove special logic for editor scenario options window
* Fix widgets not being set since page is initialized to 0
* Remove more redundant code
* Fix remaining access to widget declarations
* Remove unused variable
* Fix editor object selection tabs on successive windows
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Co-authored-by: Aaron van Geffen <aaron@aaronweb.net>
