When debugging modifier_only_shortcut_test in _waylandonly mode I saw
that it was failing, among other things, because some aspects were not
initialised.
This changes every test we have to run the new
Test::initWaylandWorkspace() that calls waylandServer()->initWorkspace()
but also makes sure that WaylandServer::initialized is emitted before we
proceed.
The layer-shell protocol allows wayland clients to create surfaces that
can be used for building desktop environment components such as panels,
notifications, etc.
The support for the plasma-shell protocol will be dropped once plasma in
all its entirety is ported to the layer-shell protocol.
