assistant2: Fix inline context picker and handle dismiss (#23081)

The new `ContextMenu`-based `ContextPicker` requires initialization when
opened, but we were only doing this for the `ContextStrip` picker, not
the inline one.

Additionally, because we have a wrapper element around ContextMenu, we
need to propagate the `DismissEvent` so that it properly closes when
Escape is pressed.

Release Notes:

- N/A

crates/assistant2/src/message_editor.rs

@@ -281,7 +281,13 @@ impl Render for MessageEditor {
                     })
                     .child(
                         PopoverMenu::new("inline-context-picker")
-                            .menu(move |_cx| Some(inline_context_picker.clone()))
+                            .menu(move |cx| {
+                                inline_context_picker.update(cx, |this, cx| {
+                                    this.init(cx);
+                                });
+
+                                Some(inline_context_picker.clone())
+                            })
                             .attach(gpui::Corner::TopLeft)
                             .anchor(gpui::Corner::BottomLeft)
                             .offset(gpui::Point {