Extend into TitleBar

[michael-hawker]

Should extend into the TitleBar with tabs, need to think on the design here a bit more.

[michael-hawker]

• Add XAML Studio name/icon as the window gripper in the TabView Footer
• Make sure to set drag region so other tab/navigation content isn't obstructed in titlebar region

[michael-hawker]

https://learn.microsoft.com/windows/uwp/ui-input/title-bar
https://learn.microsoft.com/windows/apps/design/controls/tab-view

Almost usable, seems like interacting with window then causes the input to the tabview/navview to glitch out a bit still. But otherwise is almost OK... wonder if z-ordering has to do anything, but need to make it part of TabView. Should investigate what Terminal does... @niels9001 I know you've played a bunch with this in both UWP and WinUI, I'm still in UWP land, any suggestions?

(Ah looks like Terminal has a whole custom titlebar approach: https://github.com/microsoft/terminal/blob/main/src/cascadia/TerminalApp/TitlebarControl.xaml) They may just use the tabs for the tabview control behavior vs. relying on the content area maybe? As then the tabs go in the content area of their custom titlebar... I suppose I could try similar, right now we keep each Document separate so that they each maintain their state (especially editor state) independently. It would be more memory efficient to share and rehydrate state when changing tabs (though probably slower, and wouldn't easily maintain other states of manipulated renders)... Lot more to think about here maybe if we change that overall approach. Though we could still link the Tabstrip as tabs to another containing list for current behavior.

[michael-hawker]

• Should expand the TitleBar Drag region to take up the available space the Tabs aren't taking so if you only have a tab or two you can grab the big area to drag the window.

[michael-hawker]

Fixed drag region area in 5b31fb2 - little messy, but it works. Definitely would be useful if there was an alt TitleBar that managed this tab drag stuff.

For now, this is basically done and just waiting on #3 and wrapping up the other changes.

[michael-hawker]

Done along with #3 they really ended up going hand-in-hand. dev is now the latest with this and other changes, will remove temp branch.