LibWeb: Use clip rectangles assigned to paintables in hit-testing

This change makes hit-testing more consistent in the handling of hidden
overflow by reusing the same clip-rectangles.

Also, it fixes bugs where the box is visible for hit-testing even
though it is clipped by the hidden overflow of the containing block.

Userland/Libraries/LibWeb/Painting/PaintableBox.h

@@ -210,6 +210,7 @@ protected:
     virtual CSSPixelRect compute_absolute_paint_rect() const;
 
     Optional<CSSPixelPoint> enclosing_scroll_frame_offset() const { return m_enclosing_scroll_frame_offset; }
+    Optional<CSSPixelRect> clip_rect() const { return m_clip_rect; }
 
 private:
     [[nodiscard]] virtual bool is_paintable_box() const final { return true; }