feat(linux): Allow to run ibus tests on Wayland

This change modifies the `run-tests.sh` script so that tests
run on both Wayland (if supported) and X11 unless
`--no-wayland` or `--no-x11` is specified.

This change also adds the new argument `--wayland` to the
`ibus-keyman-tests` executable which runs the tests under
Wayland.

Note that running Wayland tests is only possible in Ubuntu 21.10+
because it requires a version of `mutter` that supports the
headless option which got added in mutter 40.