QBitmap: de-inline dtor

The destructor of this polymorphic class was incorrectly marked for
removal in Qt 6, and, unfortunately, that was carried out. Now it
delivers one of the most-duplicated vtables across all of Qt (at least
four duplicates), and we can never add anything to it until Qt 7
(because existing code de-virtualized it as a no-op).

Task-number: QTBUG-45582
Pick-to: 6.3
Change-Id: I85bd3b13dca9f1fc8cb62ca079a1168a33f71323
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

src/gui/image/qbitmap.cpp

@@ -132,6 +132,12 @@ QBitmap::QBitmap(const QSize &size)
 {
 }
 
+/*!
+    \internal
+    This dtor must stay empty until Qt 7 (was inline until 6.2).
+*/
+QBitmap::~QBitmap() = default;
+
 /*!
     \fn QBitmap::clear()
 

src/gui/image/qbitmap.h

@@ -58,6 +58,7 @@ public:
     QBitmap(int w, int h);
     explicit QBitmap(const QSize &);
     explicit QBitmap(const QString &fileName, const char *format = nullptr);
+    ~QBitmap() override;
 
 #if QT_DEPRECATED_SINCE(6, 0)
     QT_DEPRECATED_VERSION_X_6_0("Use fromPixmap instead.") QBitmap &operator=(const QPixmap &);