GTK scaling issues on Steam Deck OLED

[aclist]

A user reports that certain modal dialogs appear scaled grossly out of proportion on Steam Deck OLED, notably on Game Mode. This is a variant of a GTK bug previously reported to Valve.

However, the user demonstrated (with visual proof) that the modals also get resized in Desktop Mode beyond the dimensions of the viewport.

Finally, the application itself seems to extend beyond the confines of the viewport for no discernible reason.

Lacking a Steam Deck OLED test bench, as an initial test, asked the user to try a modified version of the UI which disables window hinting and maximize parameters. Going forward, it may be best practice to not start DZGUI in fullscreen/maximized, but need to test the implications of this on Game Mode, due to its tendency to throw windows into the wrong place.