LibWeb: Make input widget (buttons, text boxes, etc) scroll with page

We now relayout all LayoutWidgets when the view is scrolled. This will
cause them to follow along with the rest of the page content.

Libraries/LibWeb/Frame.cpp

@@ -81,4 +81,18 @@ void Frame::set_needs_display(const Gfx::Rect& rect)
     on_set_needs_display(rect);
 }
 
+void Frame::did_scroll(Badge<PageView>)
+{
+    if (!m_document)
+        return;
+    if (!m_document->layout_node())
+        return;
+    m_document->layout_node()->for_each_in_subtree([&](LayoutNode& layout_node) {
+        if (layout_node.is_widget()) {
+            layout_node.layout(LayoutNode::LayoutMode::Default);
+        }
+        return IterationDecision::Continue;
+    });
+}
+
 }

Libraries/LibWeb/Frame.h

@@ -61,6 +61,8 @@ public:
     void set_viewport_rect(const Gfx::Rect&);
     Gfx::Rect viewport_rect() const { return m_viewport_rect; }
 
+    void did_scroll(Badge<PageView>);
+
 private:
     explicit Frame(PageView&);
 

Libraries/LibWeb/Layout/LayoutWidget.cpp

@@ -24,11 +24,15 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <LibGfx/Font.h>
-#include <LibGfx/StylePainter.h>
 #include <LibGUI/Painter.h>
+#include <LibGUI/ScrollBar.h>
 #include <LibGUI/Widget.h>
+#include <LibGfx/Font.h>
+#include <LibGfx/StylePainter.h>
+#include <LibWeb/DOM/Document.h>
+#include <LibWeb/Frame.h>
 #include <LibWeb/Layout/LayoutWidget.h>
+#include <LibWeb/PageView.h>
 
 namespace Web {
 
@@ -47,7 +51,11 @@ void LayoutWidget::layout(LayoutMode layout_mode)
 {
     rect().set_size(widget().width(), widget().height());
     LayoutReplaced::layout(layout_mode);
-    widget().move_to(rect().x(), rect().y());
+
+    auto adjusted_widget_position = rect().location().to_int_point();
+    if (auto* page_view = document().frame()->page_view())
+        adjusted_widget_position.move_by(-page_view->horizontal_scrollbar().value(), -page_view->vertical_scrollbar().value());
+    widget().move_to(adjusted_widget_position);
 }
 
 void LayoutWidget::render(RenderingContext& context)

Libraries/LibWeb/PageView.cpp

@@ -624,6 +624,7 @@ void PageView::dump_selection(const char* event_name)
 void PageView::did_scroll()
 {
     main_frame().set_viewport_rect(viewport_rect_in_content_coordinates());
+    main_frame().did_scroll({});
 }
 
 Gfx::Point PageView::compute_mouse_event_offset(const Gfx::Point& event_position, const LayoutNode& layout_node) const