Use the linuxdeploy GTK plugin to correctly deploy GTK3 dependencies

[cgutman]

Description

This fixes a number of errors when starting the AppImage on more modern distros than Ubuntu 20.04. We didn't bundle all the GTK3 plugins and libraries into the AppImage, so it wouldn't start. It also was missing the AppRun hook that the GTK plugin installs which allows the AppImage to run without crashing on Wayland.

This doesn't fix the issue with EGL on the AppImage, so VAAPI encoding is still unavailable. The reason for this is that the AppImage bundles libwayland-client.so which is also a dependency of libEGL_mesa.so. On a newer distro, libEGL_mesa.so may depend on symbols present on the host version of libwayland-client.so but not the older version bundled in the AppImage. The missing symbols cause libEGL_mesa.so to fail to load which causes EGL to fail.

Screenshot

Issues Fixed or Closed

Fixes #1702

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Dependency update (updates to dependencies)
• Documentation update (changes to documentation)
• Repository update (changes to repository files, e.g. .github/...)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the in code docstring/documentation-blocks for new or existing methods/components

Branch Updates

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must be updated before it can be merged. You must also
Allow edits from maintainers.

• I want maintainers to keep my branch updated