Update avifImageUsesTuneIq() after pull request #2970

[wantehchang]

@juliobbv-p Julio: I can't assign this issue to you, so I assigned it to myself as a substitute.

After pull request #2970, AOM_USAGE_ALL_INTRA may be used to encode a two-layer image item. So tune=iq may be used to encode two AV1 frames.

This means the comment "AOM_TUNE_IQ is only supported with still images in libavif and libaom as of today" at the end of the avifImageUsesTuneIq() function is no longer true:

static avifBool avifImageUsesTuneIq(const avifCodec * codec, avifBool alpha)
{
    ...

    // In practice this function should also return true if avifEncoderSetCodecSpecificOption("tune", "iq")
    // was called for a previous frame and not called (or called with NULL) for this frame, because the tune
    // option persists across frames in libaom. However AOM_TUNE_IQ is only supported with still images in
    // libavif and libaom as of today, so there is no need to remember this option across frames.
    return ret;
}

Now we need to remember the tune=iq option across frames.

[juliobbv-p]

Thanks @wantehchang for letting me know -- I'll take a look at this as my next item (and manually keep an eye on the issue). We can discuss this during our meeting tomorrow.

[juliobbv-p]

Opened #3029 to address this issue.

[wantehchang]

Fixed by Julio's PR #3029.