LibWeb: Move EditEventHandler's inclusion to EventHandler.cpp

We can get away with using the forward declaration of EditEventHandler
in the header file (and avoid ~1k rebuilt files when EditEventHandler is
modified).

There will be an upcoming DragAndDropEventHandler class, so this patch
just sets things up so that the edit and drag-and-drop event handlers
are stored the same way in EventHandler.

Userland/Libraries/LibWeb/Page/EventHandler.cpp

@@ -18,6 +18,7 @@
 #include <LibWeb/HTML/HTMLMediaElement.h>
 #include <LibWeb/HTML/HTMLVideoElement.h>
 #include <LibWeb/Layout/Viewport.h>
+#include <LibWeb/Page/EditEventHandler.h>
 #include <LibWeb/Page/EventHandler.h>
 #include <LibWeb/Page/Page.h>
 #include <LibWeb/Painting/PaintableBox.h>

Userland/Libraries/LibWeb/Page/EventHandler.h

@@ -13,7 +13,6 @@
 #include <LibJS/Heap/Cell.h>
 #include <LibJS/Heap/GCPtr.h>
 #include <LibWeb/Forward.h>
-#include <LibWeb/Page/EditEventHandler.h>
 #include <LibWeb/PixelUnits.h>
 #include <LibWeb/UIEvents/KeyCode.h>
 
@@ -35,8 +34,6 @@ public:
 
     void set_mouse_event_tracking_paintable(Painting::Paintable*);
 
-    void set_edit_event_handler(NonnullOwnPtr<EditEventHandler> value) { m_edit_event_handler = move(value); }
-
     void handle_paste(String const& text);
 
     void visit_edges(JS::Cell::Visitor& visitor) const;