qtquick Add QtQuick::Group::closeAllDockWidgets()

Can't name it close as it clashes with View::close().
Part of issue #513

src/qtquick/views/Group.cpp

@@ -280,3 +280,8 @@ void Group::setMDISize(QSize sz)
 
     layout->resizeDockWidget(m_group, sz);
 }
+
+bool Group::closeAllDockWidgets()
+{
+    return m_inDtor || m_group->close();
+}

src/qtquick/views/Group.h

@@ -69,6 +69,9 @@ class DOCKS_EXPORT Group : public QtQuick::View, public Core::GroupViewInterface
     /// Sets the size of this group in the MDI layout
     Q_INVOKABLE void setMDISize(QSize);
 
+    /// Convenience that just calls close() on all its dock widgets
+    /// Returns whether all dock widgets accepted the close
+    Q_INVOKABLE bool closeAllDockWidgets();
 
 protected:
     void removeDockWidget(Core::DockWidget *dw) override;