Adds support for concat demuxer to copy the side data information
from the input file to the resulting file. It will behave like the
metadata copy, where the metadata of the first file is kept in the
the output file.

Extract the current code that already performs the stream side_data
copy into a separate method and reuse the method in the concat demuxer.
Signed-off-by: Gerard Sole <g.sole.ca@gmail.com>