New rustdoc "Loading content..." feature breaks inbound anchors

[JohnHeitmann]

If you visit a doc page on docs from nightly with a url that includes an anchor, e.g. '.../doc/std/iter/trait.Iterator.html#method.size_hint', then the page stops loading due to a js error. The "Loading content..." messages remain forever and no doc content appears.

The js error is:

main.js:222 Uncaught TypeError: h3.getElementsByClassName is not a function
    at expandSection (main.js:222)
    at main.js:2416
    at main.js:2462

[GuillaumeGomez]

Fixed by #56876.