Update handbook layout

[adamwoodnz]

Closes #266
Depends on WordPress/wporg-mu-plugins#484 and WordPress/wporg-parent-2021#114

Widens the layout, adjusts sidebar position and pagination width, adds table styles.

NOTE: Does not include the Chapter list update

Screenshots

Full page, monitor size, with tables

Monitor	Desktop	Tablet	Mobile

Testing

1. Ensure your mu-plugins and parent branches match the dependencies listed above
2. Try loading all the handbooks and check layout, there is a list in functions.php
3. The layout goes wider than any of the other templates; the center column should keep expanding until the window reaches 1920px wide.
4. Check handbooks with long ToCs that fit in the viewport and become sticky on scroll, they should not overlap the pagination at the bottom.
5. Check the table styles, eg. theme-json-living, identified in Table styles missing for in-content tables. #235

[jasmussen]

I think this captures the conversations we had with @ndiego and @justintadlock in the Figma file, so looks good to me, but here just a ping in their direction.

[fcoveram]

The change looks fine to me 👌