Updated image viewer restructure

[CTalvio]

Pull Request Description

I used a stack to make the image viewer widget the size of the screen, which seems to be the only way to avoid the bugs the current viewer is suffering from.

Hence the scaffold and appbar get ditched in favor of simple containers for any buttons we need, stacked atop the image.

I found that layoutInsets can be used to have the initial size of the image limited to the are that is not covered by buttons.

Not in the earlier PR, here I also added prevention for images to be saved twice.

Issue Being Fixed

The inability of the image to fill the screen in some circumstances, causing it to get cut off for seemingly no reason. This was especially prevalent in landscape aspect ratios.

• Image viewer top and bottom bars can't be hidden in landscape mode #652

Screenshots / Recordings

Kooha-2024-05-03-22-54-31.mp4

Best illustrated when built into a resizable desktop app. Images always start off not covering the top and bottom bar, but when zoomed utilize the full screen.

Checklist

• Did you use localized strings (and added appropriate descriptions) where applicable?

[CTalvio]

Also tested in emulator. Correctly respects system top/bottom bars, but now always uses the full screen to display zoomed images.

Worth considering: Automatically go into the "fullscreen" mode on zoom.

[CTalvio]

Added: Dynamic fullscreen behaviour.

Above 1.2 zoom, the viewer will automatically enter the full screen mode, hiding all UI elements, now also including system.

Full screen is exited below 1.2 zoom, or if the user taps the screen without changing the zoom level.

Screen_recording_20241219_143045.mp4

[micahmo]

Wow that's really cool!