How to add custom preview options in WP 6.7

[bph]

Discussion #315

There's a new Preview Options API coming in WordPress 6.7: WordPress/gutenberg#64644 (comment)

It allows you to add custom options to the preview dropdown in the editor:

What we need is a step-by-step walkthrough of how to implement custom preview options. The API is just for adding the preview button in the dropdown, but the onClick() method (what happens when the button is clicked) is custom. We could share several different ideas on what's possible and what it could be used for.