LibWeb: Use PaintContext::would_be_fully_clipped_by_painter() everywhere

Always use `would_be_fully_clipped_by_painter` to check if painting can
be skipped.

This allows to quickly find all the places where this check happens and
also removes incosistency that before we checked for intersection with
viewport rect in some places and for intersection with painter clip
rect in other places.

Userland/Libraries/LibWeb/Painting/BackgroundPainting.cpp

@@ -316,7 +316,7 @@ void paint_background(PaintContext& context, Layout::NodeWithStyleAndBoxModelMet
             while (image_x < css_clip_rect.right()) {
                 image_rect.set_x(image_x);
                 auto image_device_rect = context.rounded_device_rect(image_rect);
-                if (image_device_rect != last_image_device_rect && image_device_rect.intersects(context.device_viewport_rect()))
+                if (image_device_rect != last_image_device_rect && !context.would_be_fully_clipped_by_painter(image_device_rect))
                     image.paint(context, image_device_rect, image_rendering);
                 last_image_device_rect = image_device_rect;
                 if (!repeat_x)

Userland/Libraries/LibWeb/Painting/PaintableBox.cpp

@@ -45,10 +45,7 @@ void PaintableBox::invalidate_stacking_context()
 
 bool PaintableBox::is_out_of_view(PaintContext& context) const
 {
-    return !context.enclosing_device_rect(absolute_paint_rect())
-                .to_type<int>()
-                .translated(context.painter().translation())
-                .intersects(context.painter().clip_rect());
+    return context.would_be_fully_clipped_by_painter(context.enclosing_device_rect(absolute_paint_rect()));
 }
 
 PaintableWithLines::PaintableWithLines(Layout::BlockContainer const& layout_box)