gst: sink: copy frames if video buffer from other pool

In case of the video, if the buffer to be rendered is from upstream and
not from the pipewirepool, map the memory into video frames and copy the
frames instead of doing a buffer copy.

Avoid splitting of buffers in the case of video, because that might break
the frame layout, especially planar formats, for the applications which
use pipewiresink as a camera source to capture video.

src/gst/gstpipewiresink.h

@@ -69,6 +69,7 @@ struct _GstPipeWireSink {
   gboolean negotiated;
   gboolean rate_match;
   gint rate;
+  gboolean is_video;
 
   GstPipeWireSinkMode mode;
   GstPipeWireSinkSlaveMethod slave_method;