wayland: Implement xdg-activation when opening urls (#11368)

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

crates/gpui/src/platform/linux/headless/client.rs

@@ -76,9 +76,10 @@ impl LinuxClient for HeadlessClient {
         unimplemented!()
     }
 
-    //todo(linux)
     fn set_cursor_style(&self, _style: CursorStyle) {}
 
+    fn open_uri(&self, _uri: &str) {}
+
     fn write_to_primary(&self, item: crate::ClipboardItem) {}
 
     fn write_to_clipboard(&self, item: crate::ClipboardItem) {}