Load `storage.js` in `rustdoc-js` and `rustdoc-js-std` test suites.

[lolbinarycat]

storage.js contains common utility methods, and we would like to be able to use those in search.js, but we can't, because storage.js is not loaded during integration testing.

Zulip Discussion

cc @GuillaumeGomez

[GuillaumeGomez]

People use our search.js file in their web browser extension. Meaning that it needs to be self contained. We can't add any external code inside the DocSearch class.