feat: reorganise editor sidebar to use tabs and new components

[thomasguillot]

All Submissions:

• Have you followed the Newspack Contributing guideline?
• Does your code follow the WordPress' coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

This PR adds a tab-like navigation, like the Group block for example, where we separate the "Settings" from the "Styles". It's a bit hacky because I couldn't find a way to do it at the document-level what we can easily achieve with the block (and simply add group="style" to a panel.

I've also tweaked some settings to use a ToggleGroupControl instead of dropdowns.

How to test the changes in this Pull Request:

Make sure all the settings etc... still work

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully ran tests with your changes locally?