Interactive hinting in TOC search box.

[csyonghe]

The current stdlib reference search box has interactive hinting:

This feature is very useful in helping users locate the correct types / functions very quickly. This is lost in readthedocs, and we should figure out how to build something similar there.

[aidanfnv]

We might be able to implement something very similar with readthedocs's search-as-you-type addon

[jkwak-work]

There is a still unresolved comment in the PR.
Since @aidanfnv will not be able to work on this until next sprint, I am pushing this to the next sprint.