D-Bus activation systemd service
Correctly scopes dolphin in systemd service app-org.kde.dolphin.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!17 (merged) to generate the dbus service file automatically