LibWeb: Obtain theme-color on meta element removal and modification

Author: https://github.com/Gingeh
Commit: 4a0ac312cc
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/3146
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/DOM/Document.h

@@ -245,6 +245,8 @@ public:
     Optional<Vector<String> const&> supported_color_schemes() const;
     void obtain_supported_color_schemes();
 
+    void obtain_theme_color();
+
     void update_style();
     void update_layout();
     void update_paint_and_hit_testing_properties_if_needed();