Fix deprecation of QMouseEvent::source() and flags()

Amends 53496e67f0b78645c6080e9218c7a36bc5a9d76d:
- move flags() out of the QT_DEPRECATED_SINCE block in the header
- add QT_DEPRECATED_SINCE block around source() implementation

Pick-to: 6.1 6.2
Change-Id: Id52fa6b04a13efbede3e6ac440060f90b283e773
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/gui/kernel/qevent.cpp

@@ -804,10 +804,12 @@ QMouseEvent::~QMouseEvent()
     \sa Qt::MouseEventSource
     \sa QGraphicsSceneMouseEvent::source()
 */
+#if QT_DEPRECATED_SINCE(6, 0)
 Qt::MouseEventSource QMouseEvent::source() const
 {
     return Qt::MouseEventSource(m_source);
 }
+#endif
 
 /*!
     \since 5.3

src/gui/kernel/qevent.h

@@ -273,8 +273,8 @@ public:
     QT_DEPRECATED_VERSION_X_6_0("Use globalPosition()")
     QPointF screenPos() const { return globalPosition(); }
     Qt::MouseEventSource source() const;
-    Qt::MouseEventFlags flags() const;
 #endif // QT_DEPRECATED_SINCE(6, 0)
+    Qt::MouseEventFlags flags() const;
 };
 
 class Q_GUI_EXPORT QHoverEvent : public QSinglePointEvent