Base layout for actions

[HadrienGardeur]

For our base layout, we'll have:

1. user settings as a partially visible, non-collapsible action
2. full screen mode as a partially visible and collapsible action
3. table of contents as a partially visible and collapsible action
4. the overflow menu as an always visible, non-collapsible action
5. jump to position as an action that's strictly displayed in the overflow menu

When actions are collapsed in the overflow menu, they retain their order. This means that on a smaller screen, our base layout will have:

• user settings
• overflow menu:
  • full screen
  • table of contents
  • jump to position

We'll also use this base layout to further test how focus and screen reader support is handled over a full implementation of actions.