AppImage: enable missing libraries

This MR brings in some changes to the AppImage build process I made as part of developing !380 (merged):

• enabling libheif
• enabling OpenJPEG, and in so doing, dropping all dependencies except LittleCMS (they are only needed for the demo binaries, not the library, and will be picked up anyway)
• fixes linking against GSL in Linux, if built from 3rdparty, by requesting the shared version of the library

Test Plan

Build an AppImage following the Binary Factory process and the changed scripts.

Formalities Checklist

• I confirmed this builds.
• I confirmed Krita ran and the relevant functions work.
• I tested the relevant unit tests and can confirm they are not broken. (If not possible, don't hesitate to ask for help!)
• I made sure my commits build individually and have good descriptions as per KDE guidelines.
• I made sure my code conforms to the standards set in the HACKING file.
• I can confirm the code is licensed and attributed appropriately, and that unattributed code is mine, as per KDE Licensing Policy.