agent: Make all icons used for tool calls consistent (#34160)

Starting to use the `Tool...` family of icons dedicated & designed for
the agent panel.

Release Notes:

- N/A

crates/assistant_tools/src/fetch_tool.rs

@@ -130,7 +130,7 @@ impl Tool for FetchTool {
     }
 
     fn icon(&self) -> IconName {
-        IconName::Globe
+        IconName::ToolWeb
     }
 
     fn input_schema(&self, format: LanguageModelToolSchemaFormat) -> Result<serde_json::Value> {