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>