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

Release Notes:

- N/A

crates/assistant_tools/src/find_replace_file_tool.rs

@@ -6,6 +6,7 @@ use project::Project;
 use schemars::JsonSchema;
 use serde::{Deserialize, Serialize};
 use std::{collections::HashSet, path::PathBuf, sync::Arc};
+use ui::IconName;
 
 use crate::replace::replace_exact;
 
@@ -135,6 +136,10 @@ impl Tool for FindReplaceFileTool {
         include_str!("find_replace_tool/description.md").to_string()
     }
 
+    fn icon(&self) -> IconName {
+        IconName::Pencil
+    }
+
     fn input_schema(&self) -> serde_json::Value {
         let schema = schemars::schema_for!(FindReplaceFileToolInput);
         serde_json::to_value(&schema).unwrap()