Doing this removes the qt6-svg dependency and allows our rasterizer to
be used for these little icons (and happens to be a fair bit smaller
than the old SVGs).
This looks a lot more "at home" than usual pixel art logo on
non-SerenityOS systems. :^)
Also, stop using site favicons as the app icon as that made it
annoyingly hard to find Ladybird in task switchers sometimes.
We now load SVG icons (via the Qt resource system) and render them into
a QIcon (with normal and disabled variants) using system colors.
We also re-render them if the system color theme changes.
This instantly makes Ladybird look less foreign on my Linux box.
I drew the icons myself, and they could definitely be more optimized,
but this was my first time using Inkscape. :^)
