feat: shim hexo-util

refer to doc https://hexo.io/api/helper#How-do-I-use-another-registered-helper-in-my-custom-helper

lib/extend/helper.ts

@@ -1,9 +1,39 @@
 import Hexo from '../hexo';
 import { PageSchema } from '../types';
+import * as hutil from 'hexo-util';
 
 interface HexoContext extends Hexo {
+  // get current page information
   // https://github.com/dimaslanjaka/hexo-renderers/blob/147340f6d03a8d3103e9589ddf86778ed7f9019b/src/helper/related-posts.ts#L106-L113
   page?: PageSchema;
+
+  // hexo-util shims
+  url_for: typeof hutil.url_for;
+  full_url_for: typeof hutil.full_url_for;
+  relative_url: typeof hutil.relative_url;
+  slugize: typeof hutil.slugize;
+  escapeDiacritic: typeof hutil.escapeDiacritic;
+  escapeHTML: typeof hutil.escapeHTML;
+  unescapeHTML: typeof hutil.unescapeHTML;
+  encodeURL: typeof hutil.encodeURL;
+  decodeURL: typeof hutil.decodeURL;
+  escapeRegExp: typeof hutil.escapeRegExp;
+  stripHTML: typeof hutil.stripHTML;
+  stripIndent: typeof hutil.stripIndent;
+  hash: typeof hutil.hash;
+  createSha1Hash: typeof hutil.createSha1Hash;
+  highlight: typeof hutil.highlight;
+  prismHighlight: typeof hutil.prismHighlight;
+  tocObj: typeof hutil.tocObj;
+  wordWrap: typeof hutil.wordWrap;
+  prettyUrls: typeof hutil.prettyUrls;
+  isExternalLink: typeof hutil.isExternalLink;
+  gravatar: typeof hutil.gravatar;
+  htmlTag: typeof hutil.htmlTag;
+  truncate: typeof hutil.truncate;
+  spawn: typeof hutil.spawn;
+  camelCaseKeys: typeof hutil.camelCaseKeys;
+  deepMerge: typeof hutil.deepMerge;
 }
 
 interface StoreFunction {