Use actual anchors for TOC links for better accessibility

[donysukardi]

Currently the TOC in the sidebar uses <label> and the route change is applied on click. It'd be better if the links are actual anchor links for accessibility reason. Users can then share direct links to different parts of the documentation.

The issue I'm facing currently is that with SSR and when the site is hydrating on the client side, the TOC links are not operational as the event handlers are still being registered.

With the change proposed above, the site would be still operational even without JavaScript.

Here's an example on how Slate does it - https://slatedocs.github.io/slate