GTK4 will remove the GtkHeaderBar:title property, so stop using it
and set the window's title property instead, as that's what headbars
use in both GTK3 and GTK4 unless explicitly overridden.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1495>
Currently there is no indication that an extension had an error except
for the sensitivity of the switch (which may have a different cause).
This is useful information to users, so add a small error indicator
alongside the updates icon and show the actual error in the details.
https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/2337
Currently the switches handle position reflects the requested
extension state (as in: the user (de)activated the switch),
while the actual extension state is reflected by the underlying
state.
That doesn't work well when the switch is insensitive though (for
example on error), because the desaturation neuters the color
that reflects the state.
Address this by resetting the switch handle to the state when
making it insensitive.
https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1263
The Extensions app code is now independent enough from the rest of the code
base to move it to its own subprojects, like we did for the extensions-tool.
This allows for stand-alone builds of the app, which we are about to use
for distributing it as flatpak.
https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1133
