libs: parser: Adds AV1 parser.

libs: parser: Adds AV1 parser.

This is the first version of AV1 parser implementation in GStreamer.

A test file is also provied with several test cases. It contains a
test sequence taken from the aom testdata set, with one key and one
inter-frame. The same test sequence has been reencoded to annexb.

testdata is taken from aom testdata (and reencoded for annexb) as well
as handcrafted testcases. Once reference testdata is available, the
testing could be imporved aswell.

Co-author: He Junyan <junyan.he@hotmail.com>
Co-author: Víctor Manuel Jáquez Leal <vjaquez@igalia.com>
Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/785>