This adds a button on the right side of the location bar to create a new
tab.
Ideally, we would actually use QTabWidget::setCornerWidget to put this
button in the tab bar. But it is surprisingly difficult to make that
look nice on all platforms. Even if we ignore macOS, the CSS to make the
button look right on KDE Plasma may not work well on Gnome. So for now,
this location next to the location bar is horizontally the same that it
would be in the tab bar at least.
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. :^)
