tests/queue-test: Add tests for proxy wrappers

Test that doing wl_display.sync on a wrapped proxy with a special queue
works as expected.

Test that creating a wrapper on a destroyed but not freed proxy fails.

Signed-off-by: Jonas Ådahl <jadahl@gmail.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>