Apply split view icons to the session context menu too.

I'd like to see helper icons for view splitting in the session context menu too. It will help with quick orientation about the expected split orientation - tested on my team members and tech course attendants.

Unfortunately - I have no environment to build the app with Kf6 right now (my distro does not have it) but based on my experience all should be fine. But I'd like to put this patch to real Kf5 powered packages too - what it the correct branch to start?

eg. extra-cmake-modules requested, requested 5.240.0, but my rolling updates distro has just 5.111.0

The patch applies to 23.08 branch