Allow using the inline assistant in prompt library (#12680)

Release Notes:

- N/A

crates/gpui/src/window.rs

@@ -1036,6 +1036,37 @@ impl<'a> WindowContext<'a> {
         });
     }
 
+    /// Subscribe to events emitted by a model or view.
+    /// The entity to which you're subscribing must implement the [`EventEmitter`] trait.
+    /// The callback will be invoked a handle to the emitting entity (either a [`View`] or [`Model`]), the event, and a window context for the current window.
+    pub fn observe<E, T>(
+        &mut self,
+        entity: &E,
+        mut on_notify: impl FnMut(E, &mut WindowContext<'_>) + 'static,
+    ) -> Subscription
+    where
+        E: Entity<T>,
+    {
+        let entity_id = entity.entity_id();
+        let entity = entity.downgrade();
+        let window_handle = self.window.handle;
+        self.app.new_observer(
+            entity_id,
+            Box::new(move |cx| {
+                window_handle
+                    .update(cx, |_, cx| {
+                        if let Some(handle) = E::upgrade_from(&entity) {
+                            on_notify(handle, cx);
+                            true
+                        } else {
+                            false
+                        }
+                    })
+                    .unwrap_or(false)
+            }),
+        )
+    }
+
     /// Subscribe to events emitted by a model or view.
     /// The entity to which you're subscribing must implement the [`EventEmitter`] trait.
     /// The callback will be invoked a handle to the emitting entity (either a [`View`] or [`Model`]), the event, and a window context for the current window.