language_model_selector: Don't recreate the Picker view each render (#21939)

While working on Assistant2, I noticed that the `LanguageModelSelector`
was recreating its `Picker` view on every single render.

This PR makes it so we create the view once and hold onto it in the
parent view.

Release Notes:

- N/A

crates/assistant2/src/terminal_inline_assistant.rs

@@ -17,7 +17,7 @@ use language::Buffer;
 use language_model::{
     LanguageModelRegistry, LanguageModelRequest, LanguageModelRequestMessage, Role,
 };
-use language_model_selector::LanguageModelSelector;
+use language_model_selector::{LanguageModelSelector, LanguageModelSelectorPopoverMenu};
 use language_models::report_assistant_event;
 use settings::{update_settings_file, Settings};
 use std::{cmp, sync::Arc, time::Instant};
@@ -439,9 +439,9 @@ enum PromptEditorEvent {
 
 struct PromptEditor {
     id: TerminalInlineAssistId,
-    fs: Arc<dyn Fs>,
     height_in_lines: u8,
     editor: View<Editor>,
+    language_model_selector: View<LanguageModelSelector>,
     edited_since_done: bool,
     prompt_history: VecDeque<String>,
     prompt_history_ix: Option<usize>,
@@ -575,17 +575,8 @@ impl Render for PromptEditor {
                     .w_12()
                     .justify_center()
                     .gap_2()
-                    .child(LanguageModelSelector::new(
-                        {
-                            let fs = self.fs.clone();
-                            move |model, cx| {
-                                update_settings_file::<AssistantSettings>(
-                                    fs.clone(),
-                                    cx,
-                                    move |settings, _| settings.set_model(model.clone()),
-                                );
-                            }
-                        },
+                    .child(LanguageModelSelectorPopoverMenu::new(
+                        self.language_model_selector.clone(),
                         IconButton::new("context", IconName::SettingsAlt)
                             .shape(IconButtonShape::Square)
                             .icon_size(IconSize::Small)
@@ -665,6 +656,19 @@ impl PromptEditor {
             id,
             height_in_lines: 1,
             editor: prompt_editor,
+            language_model_selector: cx.new_view(|cx| {
+                let fs = fs.clone();
+                LanguageModelSelector::new(
+                    move |model, cx| {
+                        update_settings_file::<AssistantSettings>(
+                            fs.clone(),
+                            cx,
+                            move |settings, _| settings.set_model(model.clone()),
+                        );
+                    },
+                    cx,
+                )
+            }),
             edited_since_done: false,
             prompt_history,
             prompt_history_ix: None,
@@ -672,7 +676,6 @@ impl PromptEditor {
             _codegen_subscription: cx.observe(&codegen, Self::handle_codegen_changed),
             editor_subscriptions: Vec::new(),
             codegen,
-            fs,
         };
         this.count_lines(cx);
         this.subscribe_to_editor(cx);