When the `org.gnome.desktop.interface` schema is not found, currently
we were not initializing the font_options which means we needed to
handle that on the backend side. Instead, generate the font_options at
that moment.
As the settings are loaded the moment we assign a backend to the
settings `_clutter_settings_set_backend` which is called just after the
backend is constructed which is too early for any actor to use it for
creating a PangoContext, so the change is safe.
Also, as the font_options getter is only used in ClutterActor when
creating the PangoContext, drop the getter. As we might just store that
info somewhere else in the future.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4106>
3153708e85