Add missing underlying type and Q_ENUM to QOpenGLWidget enums

The enums are QOpenGLWidget::UpdateBehavior and
QOpenGLWidget::TargetBuffer. The latter is a new addition to 6.5.

Pick-to: 6.5
Change-Id: I9e73413a944bf4b55e8e308055d79e560ac8668d
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

src/openglwidgets/qopenglwidget.h

@@ -24,11 +24,13 @@ public:
         NoPartialUpdate,
         PartialUpdate
     };
+    Q_ENUM(UpdateBehavior)
 
-    enum TargetBuffer {
+    enum TargetBuffer : uint8_t {
         LeftBuffer = 0,   // Default
         RightBuffer       // Only used when QSurfaceFormat::StereoBuffers is enabled
     };
+    Q_ENUM(TargetBuffer)
 
     explicit QOpenGLWidget(QWidget* parent = nullptr, Qt::WindowFlags f = Qt::WindowFlags());
     ~QOpenGLWidget();