workspace: Add clear notifications command (#13320)

Release Notes:

- Added the `workspace: clear all notifications` command to clear
notifications
([#10761](https://github.com/zed-industries/zed/issues/10761))


https://github.com/zed-industries/zed/assets/30776250/36f2c3f3-5b5e-4f98-9418-8806ce311504

crates/workspace/src/notifications.rs

@@ -191,6 +191,11 @@ impl Workspace {
         self.dismiss_notification(id, cx);
     }
 
+    pub fn clear_all_notifications(&mut self, cx: &mut ViewContext<Self>) {
+        self.notifications.clear();
+        cx.notify();
+    }
+
     fn dismiss_notification_internal(&mut self, id: &NotificationId, cx: &mut ViewContext<Self>) {
         self.notifications.retain(|(existing_id, _)| {
             if existing_id == id {