Improve prompts for tools (#11669)

Improves the descriptions for some of the tools. I wish we had metrics
to back up changes in how the model responds to tool schema changes so
anecdotally I'm just going to say this _seems_ improved.

Release Notes:

- N/A

crates/assistant2/src/assistant2.rs

@@ -19,6 +19,7 @@ use collections::HashMap;
 use completion_provider::*;
 use editor::Editor;
 use feature_flags::FeatureFlagAppExt as _;
+use file_icons::FileIcons;
 use fs::Fs;
 use futures::{future::join_all, StreamExt};
 use gpui::{
@@ -127,6 +128,12 @@ impl AssistantPanel {
                     semantic_index.project_index(project.clone(), cx)
                 });
 
+                // Used in tools to render file icons
+                cx.observe_global::<FileIcons>(|_, cx| {
+                    cx.notify();
+                })
+                .detach();
+
                 let mut tool_registry = ToolRegistry::new();
                 tool_registry
                     .register(ProjectIndexTool::new(project_index.clone()))