Add compatibility with FFMPEG 7.0

[eclipseo]

avutil: remove deprecated FF_API_REORDERED_OPAQUE

Ref: FFmpeg/FFmpeg@67e7f0b

[ilya-fedin]

This perhaps should have some replacement code rather than just commented out with 7.0+? How did upstream webrtc solve that?

[wRAR]

https://webrtc.googlesource.com/src/+/e7d10047096880feb5e9846375f2da54aef91202%5E%21/

The usage of the field in webrtc seems only to be for sanity checking, so it should be just safe to remove entirely, since webrtc does not expect re-ordering at all.

[ilya-fedin]

Ok, please replace the patch with a cherry-pick of the upstream one.

The title of the PR also sounds too loud, fixing the build usually doesn't mean adding compatibility. It usually doesn't work even after it builds and I think I heard some complains about runtime crashes with ffmpeg 7. So there's likely way more work needed for real compatibility.