LibWeb: Implement popovertarget buttons

Author: https://github.com/Gingeh
Commit: 108f3a9aac
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3285
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/AtkinsSJ

Libraries/LibWeb/DOM/Element.h

@@ -388,9 +388,16 @@ public:
         return nullptr;
     }
 
+    // An element el is in the top layer if el is contained in its node document’s top layer
+    // but not contained in its node document’s pending top layer removals.
     void set_in_top_layer(bool in_top_layer) { m_in_top_layer = in_top_layer; }
     bool in_top_layer() const { return m_in_top_layer; }
 
+    // An element el is rendered in the top layer if el is contained in its node document’s top layer,
+    // FIXME: and el has overlay: auto.
+    void set_rendered_in_top_layer(bool rendered_in_top_layer) { m_rendered_in_top_layer = rendered_in_top_layer; }
+    bool rendered_in_top_layer() const { return m_rendered_in_top_layer; }
+
     bool has_non_empty_counters_set() const { return m_counters_set; }
     Optional<CSS::CountersSet const&> counters_set();
     CSS::CountersSet& ensure_counters_set();
@@ -502,6 +509,7 @@ private:
     Array<CSSPixelPoint, 3> m_scroll_offset;
 
     bool m_in_top_layer { false };
+    bool m_rendered_in_top_layer { false };
     bool m_style_uses_css_custom_properties { false };
     bool m_affected_by_has_pseudo_class_in_subject_position { false };