quick: only forward declare QQmlV4Function

In preparation of deprecating/purging it from QQuickItem.
As a drive-by, remove a superfluous qquickpainteditem include, and move
it to the place where it is needed.

Change-Id: I42cda0a34bd5fd7b543790f75eb513303829139f
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/quick/items/context2d/qquickcanvasitem_p.h

@@ -67,6 +67,7 @@ class QQuickCanvasContext;
 
 class QQuickCanvasItemPrivate;
 class QQuickPixmap;
+class QQmlV4Function;
 
 class QQuickCanvasPixmap : public QQmlRefCount
 {

src/quick/items/qquickimplicitsizeitem_p.h

@@ -51,8 +51,8 @@
 // We mean it.
 //
 
-#include "qquickpainteditem.h"
 #include <private/qtquickglobal_p.h>
+#include <QtQuick/qquickitem.h>
 
 QT_BEGIN_NAMESPACE
 

src/quick/items/qquickloader_p.h

@@ -56,6 +56,7 @@
 QT_BEGIN_NAMESPACE
 
 class QQuickLoaderPrivate;
+class QQmlV4Function;
 class Q_QUICK_PRIVATE_EXPORT QQuickLoader : public QQuickImplicitSizeItem
 {
     Q_OBJECT

src/quick/items/qquickloader_p_p.h

@@ -62,6 +62,7 @@ QT_BEGIN_NAMESPACE
 
 
 class QQuickLoaderPrivate;
+class QQmlV4Function;
 class QQuickLoaderIncubator : public QQmlIncubator
 {
 public:

src/quick/scenegraph/qsgadaptationlayer_p.h

@@ -53,6 +53,7 @@
 
 #include <QtQuick/qsgnode.h>
 #include <QtQuick/qsgtexture.h>
+#include <QtQuick/qquickpainteditem.h>
 #include <QtCore/qobject.h>
 #include <QtCore/qrect.h>
 #include <QtGui/qbrush.h>