Accessibility: Announce client-side navigation to screen-readers by default

[luisherranz]

The enhanced Query block pagination includes a couple of screen-reader announcements, one when the page is loading (if it's taking longer than 400ms), and one after the new page has successfully loaded (code).

Astro 3.2 was released a few days ago, and they added automatic route announcements to all their client-side navigations. By the way, they do it with assertive instead of polite, which I'm not sure it's correct.

I think this is a case where announcing the next page is always going to be necessary, so we should also take a look at absorbing it inside navigate to ensure that all navigations are accessible. If something, we could make it opt-out:

await navigate(link, {
  announce: false,
});

If we don't do this for the 1.0 version, we should at least take a look at how to do it later with backward compatibility to avoid announcing the navigation twice (once inside navigate and once in the block's code).

[luisherranz]

This was included in WP 6.5.