rustdoc: Highlight methods jumped to

This helps figure out where you actually jumped to, especially if the thing you
jumped to is at the very bottom of the page.

Closes #9905
rustdoc: Fix json output and input

Turns out a hash map with integer keys isn't serializable to json.

Closes #10115
rustdoc: Clickable links on methods themselves

Useful for getting the link to a method or function.

Closes #10332
rustdoc: Handle links to reexported items

When building up our path cache, we don't plaster over a path which was
previously inserted if we're inserting a non-public-item thing.

Closes #11678