kwayland fix QMetaEnum

Hello,

the enums declared are not marked with Q_ENUM
example from plasmashell.h:
    enum class PanelBehavior {
        AlwaysVisible,
        AutoHide,
        WindowsCanCover,
        WindowsGoBelow
    };

enums not marked with Q_ENUM are not usable by few Qt convenience
classes like QMetaEnum which allows you to do:
                QMetaEnum metaEnum =
QMetaEnum::fromType<KWayland::Client::PlasmaShellSurface::PanelBehavior>();
                int value = metaEnum.keyToValue("AutoHide");
                auto m_type =
static_cast<KWayland::Client::PlasmaShellSurface::PanelBehavior>(value);
                m_plasmaShellSurface->setPanelBehavior(m_type);

declaring them with     Q_ENUM(PanelBehavior) or respective would fix
that without any side-effects I know of.

Hope you see it the same way and mark the enums with Q_ENUM

Best Regards
Damian