We can't properly parse standard Desktop files

[Aleix Pol]

Hey,
Last week I was debugging an issue where I realised that we were not
splitting properly a StringList field in a desktop file coming from
Flatpak.

I notice then that we are using a coma to split desktop files instead
of a ; as the standard requests.

The multiple values should be separated by a semicolon and the value
of the key may be optionally terminated by a semicolon. Trailing empty
strings must always be terminated with a semicolon. Semicolons in
these values need to be escaped using \;.
https://standards.freedesktop.org/desktop-entry-spec/desktop-entry-spec-latest.html

I suggested this patch, I'm not sure it's the best we can do given
we'll have to deal with quite a bit of legacy code but I'd say it's
the right thing to do.
https://phabricator.kde.org/D23381

Any thoughts?
Aleix