Optimized Slider and ProgressBar components.
Switched to the native UbuntuShapeOverlay instead of PartialColorizeUbuntuShape to render the progression in the Slider and ProgressBar components. The rendering is now faster since it removes an FBO indirection and enables batching by the QtQtuick renderer. Fixes: https://bugs.launchpad.net/bugs/1398370, https://bugs.launchpad.net/bugs/1427169.
Approved by PS Jenkins bot, Zsombor Egri.