[KIconDialog] Render SVGs with proper devicePixelRatio
SVGs can scale indefinitely, so render them crisply.
Also move all the resizing and padding into the non-SVG code path since for SVG we create the QImage ourselves so it will always have the correct dimentions, making the code easier to follow.
Verified that SVGs are rendered crisp and that PNGs are unchanged.
I don't understand why without specifying
QSvgRenderer::paint the pixmap is rendered too big (i.e. I only see a quarter, as if
QSvgRenderer didn't do high dpi properly...)