Restore AVSampleDisplayLayer renderer for dGPU/eGPU systems

These sometimes have issues importing decoded frames for Metal rendering.

app/streaming/video/ffmpeg-renderers/vt.h

@@ -4,6 +4,13 @@
 
 // A factory is required to avoid pulling in
 // incompatible Objective-C headers.
+
+class VTMetalRendererFactory {
+public:
+    static
+    IFFmpegRenderer* createRenderer();
+};
+
 class VTRendererFactory {
 public:
     static