Handle xesam:albumArtist being a string and not an array

[leosunmo]

Got tripped up by this when using https://github.com/Sinono3/souvlaki through https://github.com/jpochyla/psst.
It uses xesam:albumArtist instead of xesam:artist and the xesam:albumArtist is a String, not Array, so we should probably handle that, even if it's not convention.

Added a basic test for string vs array. Probably not the best way of doing it, but it works.

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[leosunmo]

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[soumya92]

This looks like a deviation from https://www.freedesktop.org/wiki/Specifications/mpris-spec/metadata/#xesam:albumartist.

How common is this? I would like to avoid a workaround here, but if many players are not following the spec then I'd be more open to this change.

[soumya92]

I wonder if maybe the better PR would be to just change https://github.com/Sinono3/souvlaki/blob/287797cd926fd7be802d5310fcc3836b0f5bc556/src/platform/linux/mod.rs#L303 😃

[leosunmo]

From my somewhat limited experience, most players are not quite adhering to the spec. But I agree that the proper way would be to change Souvlaki here.

[soumya92]

Okay, if its more than just this one, let's make the change. Can you also do the same for artist just to be consistent? Other than that this looks good to me.