Move VT decoding support detection into a single base class

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

@@ -2,6 +2,14 @@
 
 #include "renderer.h"
 
+#ifdef __OBJC__
+#import <Metal/Metal.h>
+class VTBaseRenderer : public IFFmpegRenderer {
+public:
+    bool checkDecoderCapabilities(id<MTLDevice> device, PDECODER_PARAMETERS params);
+};
+#endif
+
 // A factory is required to avoid pulling in
 // incompatible Objective-C headers.