LibWeb: Inspector content_size tooltip in document view

This adds a small tooltip in the browser showing the size of the
element that currently selected in the inspector view. This allows
for easier debugging since you dont have to dump the layout tree :^).

Userland/Libraries/LibWeb/Layout/Box.cpp

@@ -46,6 +46,16 @@ void Box::paint(PaintContext& context, PaintPhase phase)
         context.painter().draw_rect(enclosing_int_rect(margin_rect), Color::Yellow);
         context.painter().draw_rect(enclosing_int_rect(absolute_padding_box_rect()), Color::Cyan);
         context.painter().draw_rect(enclosing_int_rect(content_rect), Color::Magenta);
+
+        auto size_text_rect = absolute_rect();
+        auto size_text = String::formatted("{}x{}", content_rect.width(), content_rect.height());
+        size_text_rect.set_y(content_rect.y() + content_rect.height());
+        size_text_rect.set_top(size_text_rect.top());
+        size_text_rect.set_width((float)context.painter().font().width(size_text));
+        size_text_rect.set_height(context.painter().font().glyph_height());
+
+        context.painter().fill_rect(enclosing_int_rect(size_text_rect), Color::Cyan);
+        context.painter().draw_text(enclosing_int_rect(size_text_rect), size_text);
     }
 
     if (phase == PaintPhase::FocusOutline && dom_node() && dom_node()->is_element() && verify_cast<DOM::Element>(*dom_node()).is_focused()) {