Since Wayland doesn't have a way for windows to activate themselves,
currently, when you click on a link in Zed, the browser window opens in
the background.
This PR implements the `xdg-activation` protocol to get an activation
token, which the browser can use to raise its window.
https://github.com/zed-industries/zed/assets/71973804/8b3456c0-89f8-4201-b1cb-633a149796b7
Release Notes:
- N/A
