Another thread is created to execute the tests, for SetThreadDesktop to
succeed consistently. It seems to fail spuriously if it is called from
a thread that already created some windows before.

This shows that rawinput messages may be dispatched across desktops,
but only if the subscribing process has a window in the input desktop,
and it is the foreground process (even if the target window may be in
another desktop).
Signed-off-by: Rémi Bernon <rbernon@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>