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

Release Notes:

- N/A

crates/context_server/src/context_server_tool.rs

@@ -5,6 +5,7 @@ use assistant_tool::{ActionLog, Tool, ToolSource};
 use gpui::{App, Entity, Task};
 use language_model::LanguageModelRequestMessage;
 use project::Project;
+use ui::IconName;
 
 use crate::manager::ContextServerManager;
 use crate::types;
@@ -38,6 +39,10 @@ impl Tool for ContextServerTool {
         self.tool.description.clone().unwrap_or_default()
     }
 
+    fn icon(&self) -> IconName {
+        IconName::Cog
+    }
+
     fn source(&self) -> ToolSource {
         ToolSource::ContextServer {
             id: self.server_id.clone().into(),