opus.h (which is used by all the Opus code) currently includes
several structures only used by the parser and the decoder;
several elements of OpusContext are even only used by the decoder.
This commit therefore moves the part of OpusContext that is shared
between these two components (and used by ff_opus_parse_extradata())
out into a new structure and moves all the other accompanying
structures and functions to a new header, opus_parse.h; the
functions itself are also moved to a new file, opus_parse.c.
(This also allows to remove several spurious dependencies
of the Opus parser and encoder.)
Reviewed-by: Lynne <dev@lynne.ee>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
