Use dbus-update-activation-environment

The difference to ksyncdbusenv is that d-u-a-e can update systemd's
environment, too. This is only important if a userspace (dbus-daemon) bus
is used and service files make use of SystemdService to have dbus-daemon
tell systemd to start the service.

In the kernel bus (kdbus) case, systemd's environment gets updated when
org.freedesktop.dbus.UpdateActivationEnvironment is called.

REVIEW: 125768

startkde/startkde.cmake

@@ -343,7 +343,11 @@ if test -n "$PAM_KWALLET5_LOGIN" ; then
 fi
 
 # At this point all environment variables are set, let's send it to the DBus session server to update the activation environment
-@CMAKE_INSTALL_FULL_LIBEXECDIR@/ksyncdbusenv
+if which dbus-update-activation-environment >/dev/null 2>/dev/null ; then
+    dbus-update-activation-environment --systemd --all
+else
+    @CMAKE_INSTALL_FULL_LIBEXECDIR@/ksyncdbusenv
+fi
 if test $? -ne 0; then
   # Startup error
   echo 'startkde: Could not sync environment to dbus.'  1>&2

startkde/startplasmacompositor.cmake

@@ -212,7 +212,11 @@ QT_QPA_PLATFORM=wayland
 export QT_QPA_PLATFORM
 
 # At this point all environment variables are set, let's send it to the DBus session server to update the activation environment
-@CMAKE_INSTALL_FULL_LIBEXECDIR@/ksyncdbusenv
+if which dbus-update-activation-environment >/dev/null 2>/dev/null ; then
+    dbus-update-activation-environment --systemd --all
+else
+    @CMAKE_INSTALL_FULL_LIBEXECDIR@/ksyncdbusenv
+fi
 if test $? -ne 0; then
   # Startup error
   echo 'startplasmacompositor: Could not sync environment to dbus.'  1>&2