LibWeb: Add support for range deletion.

Author: https://github.com/asynts
Commit: 43dc47a494
Pull-request: https://github.com/SerenityOS/serenity/pull/4318
Reviewed-by: https://github.com/Lubrsi
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/linusg

Libraries/LibWeb/Forward.h

@@ -51,6 +51,7 @@ class MouseEvent;
 class Node;
 class ParentNode;
 class Position;
+class Range;
 class Text;
 class Timer;
 class Window;