Dbus activation systemd service
Correctly scopes spectacle in systemd service app-org.kde.spectacle.service
when dbus-activated (while still working if systemd is not present), as per https://systemd.io/DESKTOP_ENVIRONMENTS/
uses new ECM modules:
- frameworks/extra-cmake-modules!5 (merged) to simplify the systemd service templating + install
- frameworks/extra-cmake-modules!11 (closed) to generate the dbus service file automatically