Support anyOf and enum in JsonSchema (#16875)

This brings us into better alignment with the JSON schema subset that is
supported in
<https://developers.openai.com/api/docs/guides/structured-outputs#supported-schemas>,
and also allows us to render richer function signatures in code mode
(e.g., anyOf{null, OtherObjectType})

codex-rs/tools/src/js_repl_tool.rs

@@ -45,11 +45,7 @@ pub fn create_js_repl_reset_tool() -> ToolSpec {
                 .to_string(),
         strict: false,
         defer_loading: None,
-        parameters: JsonSchema::Object {
-            properties: BTreeMap::new(),
-            required: None,
-            additional_properties: Some(false.into()),
-        },
+        parameters: JsonSchema::object(BTreeMap::new(), /*required*/ None, Some(false.into())),
         output_schema: None,
     })
 }