fix(v2): Consistently use require.resolve in official plugins to resolve modules (#2797)

* fix(v2): Use require.resolve to resolve loaders in official plugins

* Use require.resolve to resolve client modules

packages/docusaurus-theme-bootstrap/src/index.js

@@ -14,7 +14,7 @@ module.exports = function () {
       return path.resolve(__dirname, './theme');
     },
     getClientModules() {
-      return ['bootstrap/dist/css/bootstrap.min.css'];
+      return [require.resolve('bootstrap/dist/css/bootstrap.min.css')];
     },
   };
 };