QmlJsInspector: remove private header dependencies

A copy of the client debugging code is made in src/libs/qmljsdebugclient/
(this comes from the qt code from commit 65642dd343bf61)

So the qmljsinspector plugin does not require anymore Qt private headers.

src/plugins/qmljsinspector/qmljslivetextpreview.h

@@ -33,12 +33,11 @@
 #include <QObject>
 #include <QWeakPointer>
 
-#include <private/qdeclarativedebug_p.h>
 #include <qmljs/parser/qmljsastfwd_p.h>
 #include <qmljs/qmljsdocument.h>
+#include "qmljsprivateapi.h"
 
 QT_FORWARD_DECLARE_CLASS(QTextDocument)
-QT_FORWARD_DECLARE_CLASS(QDeclarativeDebugObjectReference)
 
 namespace Core {
     class IEditor;