window tracker: update docs on chromium shortcuts

The format of the .desktop file names and their StartupWMClass of Chromium and Chrome shortcuts has changed, so update the docs to match the most recent versions of these web browsers. I used Looking Glass to confirm these changes to WM_CLASS:

The user interface to create shortcuts has also changed. They are no longer created through a "Tools" menu (which doesn't exist anymore), but rather through a "Save and share" menu, as shown in the screenshot below. So add that to the docs as well.

Finally, replace the examples using the GNOME Wiki with examples using the new GNOME Developer Handbook.

Fixes #7482 (closed)