cue-sheet: Read files as converted to UTF-8

This allows to parse CUE sheets encoded in UTF-8, UTF-16BE, UTF-16LE,
UTF-32BE or UTF-32LE.

https://gitlab.gnome.org/GNOME/gnome-games/issues/19
2 jobs for wip/aplazas/unicode in 49 minutes and 37 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Build Flatpak
passed flatpak:gnome-games #31529

00:49:13

passed flatpak:unit-tests #31528

00:06:13