Prefer FFmpeg for all formats except FLAC/OGG

Is there an inherit limitation in FFmpeg that prevents using it for FLAC, Vorbis, and Opus? Are there upstream bug reports about the limiting factors?

Decoding tests don't pass for FLAC and OGG, seeking seems to be buggy, all documented in code comments. The native libraries work (almost) flawlessly.

We could use FFmpeg for OPUS instead of the native decoder as I just noticed, all tests pass. I remember that this required raising the bounds for allowed decoding errors slightly.

Decoding WavPack files also works, so we don't necessarily need to keep SoundSourceWv for the 1 or 2 people who might still use it.

        ///////////////////////////////////////////////////////////
        // Codecs with failing tests
        ///////////////////////////////////////////////////////////
        /*
    } else if (!strcmp(pavInputFormat->name, "flac")) {
        // FFmpeg failure causes test failure:
        // [flac @ 0x2ef2060] read_timestamp() failed in the middle
        // SoundSourceFFmpeg - av_seek_frame() failed: Operation not permitted
        list.append("flac");
        continue;
    } else if (!strcmp(pavInputFormat->name, "ogg")) {
        // Test failures that might be caused by FFmpeg bug:
        // https://trac.ffmpeg.org/ticket/3825
        list.append("ogg");
        continue;

Perhaps we could drop all SoundSources besides FFmpeg and libsndfile once https://github.com/libsndfile/libsndfile/issues/643 is fixed.

Unless we have a way to determine encoder sample offsets, this will potentially invalidate all existing cue points.

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/10313