avformat/mov: add support for tile HEIF still images

Export each tile as its own stream, and the grid information as a Stream Group
of type TILE_GRID.
This also enables exporting other stream items like thumbnails, which may be
present in non tiled HEIF images too. For those, the primary stream will be
tagged with the default disposition.

Based on a patch by Swaraj Hota

Signed-off-by: James Almer <jamrial@gmail.com>

libavformat/internal.h

@@ -637,6 +637,11 @@ void ff_remove_stream(AVFormatContext *s, AVStream *st);
  * is not yet attached to an AVFormatContext.
  */
 void ff_free_stream_group(AVStreamGroup **pstg);
+/**
+ * Remove a stream group from its AVFormatContext and free it.
+ * The stream group must be the last stream group of the AVFormatContext.
+ */
+void ff_remove_stream_group(AVFormatContext *s, AVStreamGroup *stg);
 
 unsigned int ff_codec_get_tag(const AVCodecTag *tags, enum AVCodecID id);