timeLimitsManager: Integrate with malcontent and lock when limit reached

timeLimitsManager: Integrate with malcontent and lock when limit reached

Lock the screen when screen time limit is reached in a child session,
which required extending the existing TimeLimitsManager functionality to
include the parental controls session limits.

TimeLimitsDispatcher was also adjusted to take into account parental
controls session limits before making any user facing changes.

Closes: https://gitlab.gnome.org/GNOME/gnome-shell/-/work_items/8575
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3841>