assistant tools: Add Tool::icon method instead of matching on name (#27444)

Release Notes:

- N/A

crates/assistant_tools/src/diagnostics_tool.rs

@@ -11,6 +11,7 @@ use std::{
     path::{Path, PathBuf},
     sync::Arc,
 };
+use ui::IconName;
 
 #[derive(Debug, Serialize, Deserialize, JsonSchema)]
 pub struct DiagnosticsToolInput {
@@ -45,6 +46,10 @@ impl Tool for DiagnosticsTool {
         include_str!("./diagnostics_tool/description.md").into()
     }
 
+    fn icon(&self) -> IconName {
+        IconName::Warning
+    }
+
     fn input_schema(&self) -> serde_json::Value {
         let schema = schemars::schema_for!(DiagnosticsToolInput);
         serde_json::to_value(&schema).unwrap()