Linux/CI: Switch to Ubuntu 22.04 and linuxdeploy

[stenzek]

Description of Changes

Moves the Linux builder to Ubuntu 22.04 so we can use C++20.

Switches from manual AppImage creation to using linuxdeploy, but we have to do some post steps because the Qt plugin there doesn't support Wayland... of frickin course. Gotta love the Linux desktop experience.

Adds libstdc++ into the appimage so hopefully it'll still run on Ubuntu 20.04. With any luck the libc is the same.....

Rationale behind Changes

Moves the Linux builder to Ubuntu 22.04 so we can use C++20.

Suggested Testing Steps

Make sure AppImage works on a few distros in both brokeland and xorg.