MediaViewer: Add zoom levels

This adds the same zoom levels that Eye of GNOME has.

See https://gitlab.gnome.org/World/fractal/issues/265
1 job for improve-zoom in 20 minutes and 18 seconds (queued for 27 minutes and 11 seconds)
latest
Status Job ID Name Coverage
  Test
passed #63124
flatpak

00:20:18