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/context_picker.rs

@@ -65,14 +65,15 @@ impl ContextPicker {
         }
     }
 
-    pub fn reset_mode(&mut self, cx: &mut ViewContext<Self>) {
-        self.mode = ContextPickerMode::Default(self.build(cx));
+    pub fn init(&mut self, cx: &mut ViewContext<Self>) {
+        self.mode = ContextPickerMode::Default(self.build_menu(cx));
+        cx.notify();
     }
 
-    fn build(&mut self, cx: &mut ViewContext<Self>) -> View<ContextMenu> {
+    fn build_menu(&mut self, cx: &mut ViewContext<Self>) -> View<ContextMenu> {
         let context_picker = cx.view().clone();
 
-        ContextMenu::build(cx, move |menu, cx| {
+        let menu = ContextMenu::build(cx, move |menu, cx| {
             let kind_entry = |kind: &'static ContextKind| {
                 let context_picker = context_picker.clone();
 
@@ -90,11 +91,24 @@ impl ContextPicker {
                 .enumerate()
                 .map(|(ix, entry)| self.recent_menu_item(context_picker.clone(), ix, entry));
 
-            menu.when(has_recent, |menu| menu.label("Recent"))
+            let menu = menu
+                .when(has_recent, |menu| menu.label("Recent"))
                 .extend(recent_entries)
                 .when(has_recent, |menu| menu.separator())
-                .extend(ContextKind::all().into_iter().map(kind_entry))
+                .extend(ContextKind::all().into_iter().map(kind_entry));
+
+            match self.confirm_behavior {
+                ConfirmBehavior::KeepOpen => menu.keep_open_on_confirm(),
+                ConfirmBehavior::Close => menu,
+            }
+        });
+
+        cx.subscribe(&menu, move |_, _, _: &DismissEvent, cx| {
+            cx.emit(DismissEvent);
         })
+        .detach();
+
+        menu
     }
 
     fn select_kind(&mut self, kind: ContextKind, cx: &mut ViewContext<Self>) {