LibWeb: Support CSS floats in inline flow

CSS floats are now emitted by the InlineLevelIterator. When this
happens, IFC coordinates with the parent BFC to float the box to the
side, using the current LineBuilder state for vertical placement.

This makes the "instructions" text on Acid3 render as a single
contiguous flow of inline content.

Userland/Libraries/LibWeb/Layout/InlineLevelIterator.h

@@ -27,6 +27,7 @@ public:
             Element,
             ForcedBreak,
             AbsolutelyPositionedElement,
+            FloatingElement,
         };
         Type type {};
         Layout::Node const* node { nullptr };