ApplicationScreenshots: Improve visuals and behavior

• Using new WheelHandler features instead of ScrollView to stop eating wheel events when trying to scroll vertically.
  • Depends on frameworks/kirigami!415 (merged)
  • When scrolling vertically through the horizontal list view with a touchpad on Wayland, scrolling is really slow and seems to only move in small increments. I have no idea why this is, but it has nothing to do with ScrollView or WheelHandler. Even If you use neither, the issue remains, so maybe it's a Flickable problem? Oddly, a mouse is perfectly fine. On X11, touchpads behave just fine. Maybe it has something to do with QWheelEvent::phase()? There is no ScrollPhase set on X11 for touchpad QWheelEvents, but Wayland uses ScrollBegin, ScrollUpdate and ScrollEnd.
• No more horizontal scrollbar. Having it there looked kind of ugly and it didn't seem that necessary. The next/previous buttons indicate if you're at the beginning or end. You can scroll horizontally with Alt + a vertical wheel (like Qt Widgets), a horizontal wheel, a touchpad or by flicking if you're not using a mouse/touchpad.
• Horizontal scrolling with a mouse should be less jittery now. Touchpads are a bit bugged on Wayland though.
• Next/previous buttons in the ListView now jump to the image nearest to or just outside of the edges.
• ListView now has some margins on the left and right in the parent layout.
• Animations from clicking the left/right buttons are a bit faster and rely on standard durations now.
• ListView is now pixelAligned
• Some accessibility info has been set. Not super descriptive since a screenshots listview is mostly useless for blind people, it just says what kinds of UI components are being used.
• Shortcuts are mirrored with mirrored layouts
• Using asynchronous for all images to improve page load times
• Smoother, faster and more RAM efficient screenshot thumbnails
• Navigation for popup and thumbnail list view are now separate
• You can now click anywhere to close the popup.
• No more background for the popup, instead using a darker overlay.
• Next/previous buttons in the listview disappear when the popup appears so that they can't be confused with the identical looking popup next/previous buttons.

@teams/vdg @teams/usability

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