Ladybird: Use custom QIconEngine to render scalable/vector icons

Rather than render the icons to a 16x16 bitmap, keep them as vector
graphics and render them on request. This keeps the icons crisp on high
DPI displays.

Ladybird/CMakeLists.txt

@@ -91,6 +91,7 @@ set(SOURCES
     Settings.cpp
     SettingsDialog.cpp
     Tab.cpp
+    TVGIconEngine.cpp
     Utilities.cpp
     WebContentView.cpp
     ladybird.qrc