ProgressBar: implement styling for indeterminate mode
The existing Breeze QStyle implementation uses a series of moving rectangles that are clipped into a rectangle with rounded corners. Unfortunately we can't reimplement this because QML does not support non-rectangular clipping. See https://bugreports.qt.io/browse/QTBUG-9008.
Instead we use a series of moving pills, which looks quite nice IMO.
The 14px indicator size was taken from here https://invent.kde.org/plasma/breeze/-/blob/master/kstyle/breezemetrics.h#L113
Closes #20 (closed).
Edited by Jack Hill