Return format as specified in original QWindow

Overload QPlatformWindow::format() to return the desired format
defined in the QWindow. This is required for windows that define
specific surface formats (such as those used in Qt3d which require
a depth buffer).

This is similar to what is done in the OS X Cocoa QPA plugin.

Change-Id: I7661a2a9c4e13603d03d3a5be10d000f73c712e6
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

src/plugins/platforms/ios/qioswindow.h

@@ -80,6 +80,8 @@ public:
 
     void clearAccessibleCache();
 
+    QSurfaceFormat format() const Q_DECL_OVERRIDE;
+
 private:
     void applicationStateChanged(Qt::ApplicationState state);
     void applyGeometry(const QRect &rect);

src/plugins/platforms/ios/qioswindow.mm

@@ -93,6 +93,13 @@ QIOSWindow::~QIOSWindow()
     [m_view release];
 }
 
+
+QSurfaceFormat QIOSWindow::format() const
+{
+    return window()->requestedFormat();
+}
+
+
 bool QIOSWindow::blockedByModal()
 {
     QWindow *modalWindow = QGuiApplication::modalWindow();