Utils: More forward declarations / drop unused headers [H-K]

Round 1 - focus on headers.
For classes with initial in range [H-K].
Try to keep the same separators between different kind of headers.

Change-Id: Iefb032953743be41a847ee011c30527edfa425d8
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/plugins/scxmleditor/plugin_interface/actionhandler.cpp

@@ -24,6 +24,7 @@
 ****************************************************************************/
 
 #include "actionhandler.h"
+
 #include "mytypes.h"
 
 #include <utils/utilsicons.h>