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
