joystick: Don't use udev in Flatpak or pressure-vessel container Flatpak[1] and pressure-vessel[2] are known to use user namespaces, therefore udev event notification via netlink won't work reliably. Both frameworks provide a filesystem API that libraries can use to detect them. Do that, and automatically fall back from udev-based device discovery to the inotify-based fallback introduced in Bug #5337. [1] <https://flatpak.org/> [2] <https://gitlab.steamos.cloud/steamrt/steam-runtime-tools/-/tree/master/pressure-vessel> Signed-off-by: Simon McVittie <smcv@collabora.com>