Multiple fixes and updates for the gnome stack

Most remarkably:

community/gnome-session: remove unnecessary patch

The issue upstream[1] has been fixed through[2]

[1] https://gitlab.gnome.org/GNOME/gnome-session/-/issues/44
[2] https://github.com/elogind/elogind/pull/142

community/mutter: add xwayland depencency explicitly

@Newbyte, I believe the last commit is what could have caused Nikita to get an installation with missing icons. Waiting for your feedback to undraft. Actually, according to docs the triggers are always executed at the end. So the cache should always be populated, since the evaluation is deferred until the installation is finished.