add: api.utils.ExtraField

resolve: #336

Author: windingwind

src/api.ts

@@ -4,6 +4,7 @@ import {
   dispatchActionByShortcut,
 } from "./modules/dispatch";
 import { ClipboardHelper } from "zotero-plugin-toolkit/dist/helpers/clipboard";
+import { ExtraFieldTool } from "zotero-plugin-toolkit/dist/tools/extraField";
 import { getActions, updateAction, deleteAction } from "./utils/actions";
 
 const actionManager = {
@@ -17,6 +18,7 @@ const actionManager = {
 
 const utils = {
   ClipboardHelper,
+  ExtraField: new ExtraFieldTool(),
 };
 
 export default {