Enable overriding video sink release op (completes video sink customization API)

src/VideoManager/VideoManager.cc

@@ -71,7 +71,7 @@ VideoManager::~VideoManager()
         }
 #if defined(QGC_GST_STREAMING)
         if (_videoSink[i] != nullptr) {
-            GStreamer::releaseVideoSink(_videoSink[i]);
+            qgcApp()->toolbox()->corePlugin()->releaseVideoSink(_videoSink[i]);
             _videoSink[i] = nullptr;
         }
 #endif

src/api/QGCCorePlugin.cc

@@ -485,6 +485,15 @@ void* QGCCorePlugin::createVideoSink(QObject* parent, QQuickItem* widget)
 #endif
 }
 
+void QGCCorePlugin::releaseVideoSink(void* sink)
+{
+#if defined(QGC_GST_STREAMING)
+    GStreamer::releaseVideoSink(sink);
+#else
+    Q_UNUSED(sink)
+#endif
+}
+
 bool QGCCorePlugin::guidedActionsControllerLogging() const
 {
     return GuidedActionsControllerLog().isDebugEnabled();

src/api/QGCCorePlugin.h

@@ -119,6 +119,8 @@ public:
     virtual VideoReceiver* createVideoReceiver(QObject* parent);
     /// Allows the plugin to override the creation of VideoSink.
     virtual void* createVideoSink(QObject* parent, QQuickItem* widget);
+    /// Allows the plugin to override the release of VideoSink.
+    virtual void releaseVideoSink(void* sink);
 
     /// Allows the plugin to see all mavlink traffic to a vehicle
     /// @return true: Allow vehicle to continue processing, false: Vehicle should not process message