QDebugStateSaver: port from QScopedPointer to unique_ptr

In preparation of adding QT_NO_SCOPED_POINTER, which would be rather
pointless for users if public headers continued to mention the type.

Pick-to: 6.9 6.8
Task-number: QTBUG-132213
Change-Id: Ib5a40a1b8defe1cfe858218bb25c422f900dfe6b
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qdebug.h

@@ -333,7 +333,7 @@ public:
     ~QDebugStateSaver();
 private:
     Q_DISABLE_COPY(QDebugStateSaver)
-    QScopedPointer<QDebugStateSaverPrivate> d;
+    std::unique_ptr<QDebugStateSaverPrivate> d;
 };
 
 class QNoDebug