Actions and packaging improvements

TODO:

• Output binaries for macOS builds
• macOS multiarchitecture (universal) build:
  • We have abandoned the idea of implementing it ourselves, see the discussion in #2046. Feel free to submit a PR if you want to add the support for this
  • https://stackoverflow.com/questions/5334095/cmake-multiarchitecture-compilation
  • https://cmake.org/cmake/help/latest/manual/cmake-toolchains.7.html#id27
  • https://github.com/leetal/ios-cmake
• Haiku build support:
  • Implemented using Haiku in a VM instead of using cross-compilation toolset below due to inability to install packages in a convenient way
  • To use in GitHub Actions: container: 'haiku/cross-compiler:x86_64-r1beta4' (https://hub.docker.com/r/haiku/cross-compiler)
  • https://github.com/haiku/haiku-toolchains-ubuntu
  • https://www.haiku-os.org/docs/develop/packages/README.html
  • https://jessicah.github.io/haiku-notes.html
  • https://jessicah.github.io/building-rust.html
  • https://github.com/kaidokert/scummvm-buildbot/blob/a6be13f7922466b576c998e80f9e1bf9d3a601f3/workers/haiku/Dockerfile
• Merge bsd job into cmake job once https://github.com/cross-platform-actions/action/issues/83 is done

Packaging:

• Provide AppImage package
  • Since version 4.2, CMake has built-in AppImage generator
  • https://github.com/Ravbug/AppImage.cmake
• Provide Flatpak package (#1050)
• DEB packages
  • Merge package metadata in debian folder into cmake/XRay.Packaging.cmake
    • Some preliminary work and optimizations are made in #1953
  • Provide automated updates for our PPA on launchpad
• RPM packages
  • #1044
• Provide README.txt in packages and archives for better readability
  • Can use Pandoc for automatic conversion: pandoc -f markdown -t plain README.md -o README.txt.
    • Can either be installed directly or used from a container
  • Another alternative is https://github.com/ejrbuss/markdown-to-txt, but Pandoc is superior.

Useful links:

• https://askubuntu.com/questions/16446/how-to-get-my-software-into-ubuntu
• https://wiki.ubuntu.com/UbuntuDevelopment/NewPackages
• https://repology.org/project/openxray/versions