chore(STEM): add a ALAC stem test file

[acolombier]

FYI, this is how the file was generated, in order to be stricly equivalent to the existing AAC version (./src/test/stems/test.stem.mp4)

ffmpeg -i ./src/test/stems/test.stem.mp4 -map 0:0 -c:a alac main.m4a
ffmpeg -i ./src/test/stems/test.stem.mp4 -map 0:1 -c:a alac drum.m4a
ffmpeg -i ./src/test/stems/test.stem.mp4 -map 0:2 -c:a alac bass.m4a
ffmpeg -i ./src/test/stems/test.stem.mp4 -map 0:3 -c:a alac other.m4a
ffmpeg -i ./src/test/stems/test.stem.mp4 -map 0:4 -c:a alac vocal.m4a
docker run -v `pwd`:`pwd` -w `pwd` -it --rm aclmb/stemgen:main create \
    --mastered main.m4a \
    --drum drum.m4a \
    --bass bass.m4a \
    --other other.m4a \
    --vocal vocal.m4a \
    --codec alac \
    --drum-stem-color '#fd4a4a' \
    --bass-stem-color '#ffff00' \
    --other-stem-color '#00e8e8' \
    --vocal-stem-color '#ad65ff' \
    --other-stem-label Synths \
    --vocal-stem-label Vox \
    ./src/test/stems/test_alac.stem.mp4

Closes #15317 and #15384

[JoergAtGithub]

We should test on all platforms with both formats.

[JoergAtGithub]

LGTM! Thank you!