lomiri greeter: in usageMode 'desktop' the OSK reserves space for the launcher (which is not shown)

How to reproduce this issue:

• Install Debian 13 minimal on physical hardware (e.g. a notebook) or a VM, and run apt install lomiri afterwards. Reboot.
• This issue happens in Lomiri Greeter, so don't log into the Lomiri session.
• Click on the keyboard icon in the username / password prompt of the greeter
• Observe.
• As a 2nd step: Then switch to a TTY and add this content:

[com.lomiri.Shell]
usage-mode='Staged'

to a new file named /usr/share/glib2.0/schemas/99_lomiri.override

• Run glib-compile-schemas /usr/share/glib2.0/schemas to activate the new override.
• Restart LightDM (invoke-rc.d lightdm restart)

What you will observe:

• The OSK comes up and does not spread across the whole width of the display, there is a gap on the left side, matching the size of the Lomiri Launcher (which is not shown)
• After you have enforced the window manager mode to "Staged", OSK spreads across the whole width of the screen.

What should happen:

In 'windowed' or Desktop mode, the OSK should always spread across the whole width of the screen if the launch is not shown. In Lomiri, there is a concept for showing the launcher even in full greeter mode (for session broadcasting). The session broadcasting feature is currently broken / was never fully implemented by Canonical Ltd. (we disabled the corresponding unit test due to that, see [1]).

[1] https://gitlab.com/ubports/development/core/lomiri/-/commit/00baa3c563c12a119e9a2857c8aa50c908b9ab33

See: