react-loadable fix webpack/node.js compatibility (#39033)

* Update index.d.ts

According to  webpack types
https://github.com/DefinitelyTyped/DefinitelyTyped/blob/f58986ca20210f8e6612942db077b9228740a315/types/webpack-env/index.d.ts#L44

this returns array of strings in node.js and array of numbers in webpack.

* Update index.d.ts

use Array for non simple types

types/react-loadable/index.d.ts

@@ -66,7 +66,7 @@ declare namespace LoadableExport {
          * });
          * ```
          */
-        webpack?: () => number[];
+        webpack?: () => Array<string | number>;
     }
 
     interface OptionsWithoutRender<Props> extends CommonOptions {