Wire up AssistantPanelDelegate based on assistant2 feature flag (#23444)

This PR adjusts how the `AssistantPanelDelegate` global is set to be
based on the state of the feature flag.

This should prevent `assistant` and `assistant2` from potentially
clobbering each other.

Release Notes:

- N/A

crates/zed/src/zed.rs

@@ -12,6 +12,7 @@ pub(crate) mod windows_only_instance;
 use anyhow::Context as _;
 pub use app_menus::*;
 use assets::Assets;
+use assistant_context_editor::AssistantPanelDelegate;
 use breadcrumbs::Breadcrumbs;
 use client::{zed_urls, ZED_URL_SCHEME};
 use collections::VecDeque;
@@ -458,10 +459,20 @@ fn initialize_panels(prompt_builder: Arc<PromptBuilder>, cx: &mut ViewContext<Wo
             //
             // Once we ship `assistant2` we can push this back down into `assistant2::assistant_panel::init`.
             if is_assistant2_enabled {
+                <dyn AssistantPanelDelegate>::set_global(
+                    Arc::new(assistant2::ConcreteAssistantPanelDelegate),
+                    cx,
+                );
+
                 workspace
                     .register_action(assistant2::AssistantPanel::toggle_focus)
                     .register_action(assistant2::InlineAssistant::inline_assist);
             } else {
+                <dyn AssistantPanelDelegate>::set_global(
+                    Arc::new(assistant::assistant_panel::ConcreteAssistantPanelDelegate),
+                    cx,
+                );
+
                 workspace
                     .register_action(assistant::AssistantPanel::toggle_focus)
                     .register_action(assistant::AssistantPanel::inline_assist);