We got the indicator out of the business of tracking connections,
now it's time to do the same for devices.
Let sections track device additions and removals, and create device
items for them as it sees fit.
It also allows the sections to handle the ::activation-failed signal
by themselves, instead of passing it on from device items.
With this, the indicator is now solely responsible for global state:
Manage the top bar indicators, notify on connection failures, and run
the portal helper when NetworkManager detects a captive portal.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2407>
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