reworked how shaped windows with svg backgrounds are obtained:
there is a new function PanelSvg::mask() that returns a qbitmap of the areas of the svg with alpha=0 that can be used to create the mask of the window, at the moment used in tooltip and dialog (krunner still to come).

so now windows that uses svg backgrounds should always set PanelSvg::mask() as their own mask, regardless if composite is active or not.In this commit there are also two (identical) svgs for opaque tooltips and dialogs with pixelated rounded borders that looks good without antialiasing (and unlike the previous version they are vector based now).