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

Release Notes:

- N/A

crates/assistant_tools/src/thinking_tool.rs

@@ -7,6 +7,7 @@ use language_model::LanguageModelRequestMessage;
 use project::Project;
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
+use ui::IconName;
 
 #[derive(Debug, Serialize, Deserialize, JsonSchema)]
 pub struct ThinkingToolInput {
@@ -30,6 +31,10 @@ impl Tool for ThinkingTool {
         include_str!("./thinking_tool/description.md").to_string()
     }
 
+    fn icon(&self) -> IconName {
+        IconName::Brain
+    }
+
     fn input_schema(&self) -> serde_json::Value {
         let schema = schemars::schema_for!(ThinkingToolInput);
         serde_json::to_value(&schema).unwrap()