avformat/mov: Expose encryption info to the app.

This exposes encryption info from the container to the app.  This
includes key ID, IV, and subsample byte ranges.  The info is passed
using the new side-data AV_PKT_DATA_ENCRYPTION_DATA and
AV_PKT_DATA_ENCRYPTION_INIT_DATA.

Signed-off-by: Jacob Trimble <modmaker@google.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>