Fix the build: add missing #includes

<QWidget> for QWidget, <QDataStream> for QDataStream and <QMetaObject>
for Q_GADGET (technically, qobjectdefs.h)

Change-Id: Ia7e8b12ff4c67827bb7782a0337714e330de1db1
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
Reviewed-by: hjk <hjk121@nokiamail.com>

src/libs/qmljs/qmljscodeformatter.h

@@ -38,6 +38,7 @@
 #include <QStack>
 #include <QList>
 #include <QVector>
+#include <QMetaObject>
 
 QT_BEGIN_NAMESPACE
 class QTextDocument;