Switch to Slint Circular Progress Bar

[Vadoola]

Once Slint paths support line caps (slint-ui/slint#4676) remove the SVG progress circle and switch to a pure slint component.

[Vadoola]

In the discussion I had initially created asking if Line Caps would be supported, someone made a recommendation I hadn't considered. Essentially drawing the whole circular progress bar using a path, including a rounded end. They even provided a working example. It's not quite as clean as just a single line with a thickness and a line cap, but it probably is better than the SVG. It's a Slint component, it's one less file to include I should be able to animate the progress property to make the progress circle animate smoothly with a lower resolution timer, which will probably give better performance.