Display an empty Wi-Fi icon when the Wi-Fi is not connected

When doing usability test for Tails, I often see people take some time to find out that they need to click in the top-right corner of the desktop to connect to a Wi-Fi network.

Displaying an empty Wi-Fi icon even when the Wi-Fi is not connected would provide a visual clue on where to find this core feature of the OS.

This issue is a learnability and discoverability issue and would mostly affect first time users. In the case of Tails, most of our users are not otherwise Linux users so it's a bit more severe but I think that it's in the interest of GNOME in general to ease to experience of first time users as we want many more of them :)

For example, that's how macOS does it too:

Wi-Fi being by far the most common option for people to connect to the Internet these day, I think that it deserves some visibility on the desktop by default. The empty icon could also be displayed only when a Wi-Fi interface is being detected and not otherwise.