decoder: Use glycin for decoding

Merged Sophie Herold requested to merge wip/sophie-h/glycin into main
  • Finish glycin
  • Make animations work
  • Use formats supplied by glycin
  • Implement unsupported format info
  • Install glycin via flatpak manifest
  • Disable sandbox for devel but not nightly
  • Get glycin-heif to build

Closes #72 (closed), #159 (closed), #162 (closed), #163 (closed)

Edited by Sophie Herold

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