Full xdg_activation_v1 support

Now that the protocol is merged, I'm creating this issue to keep track of the many aspects that fit into this bigger picture.

Bare minimum to claim Plasma supports it:

• KWayland Server: kwayland-server!130 (merged)
• KWin's implementation: !434 (merged)
• Plasma (KRun?) token exchange
  • StartupNotify=false should not pass an app_id so we don't get any notification
• Pass token when triggering from a notification (protocol change https://gitlab.freedesktop.org/xdg/xdg-specs/-/merge_requests/43)
• Plasma Window Manager protocol (?) startup notifications
• StatusNotifierItems should be provided an activation token when an action is triggered

Apps:

• Qt 6 client support: https://codereview.qt-project.org/c/qt/qtwayland/+/321246
• Qt5/KF5 support, even if ad-hoc API
• KDBusService::activateRequested
• GTK: https://gitlab.gnome.org/GNOME/gtk/-/merge_requests/3502