Include Wayland platform plugin in AppImage

[askmeaboutlo0m]

The AppImage currently only includes the platform plugin for X11, which means that running it on Wayland won't work.

There's a branch feature/qtwayland that builds the platform plugin, but that's not enough to actually make it work, since linuxdeploy-plugin-qt won't include it and apparently there's no way to actually make it do that without changes to the plugin.

There's an open issue linuxdeploy/linuxdeploy-plugin-qt#160 and a pull request linuxdeploy/linuxdeploy-plugin-qt#157 over there that implements it, so it's probably sensible to just wait for that to be resolved upstream than to build our own patched version of the plugin.

The workaround is to use the Flatpak version or to just compile Drawpile from source, which is not that big a deal on Linux.

[askmeaboutlo0m]

Tablet cursors on Wayland are currently busted in various ways, see upstream bugs https://bugs.kde.org/show_bug.cgi?id=477570 and https://gitlab.gnome.org/GNOME/mutter/-/issues/2983. That makes Wayland not really usable in the first place, we'd have to patch Qt first. So that lowers the priority on this even further, since users are likely going to have to switch to X11 anyway.