Navigation block erroneously requests /wp/v2/block-navigation-areas in WP 5.9

[noisysocks]

Description

The Navigation block is making a request to /wp/v2/block-navigation-areas.

gutenberg/packages/block-library/src/navigation/edit/index.js

Lines 112 to 117 in 2655693

	const [ areaMenu, setAreaMenu ] = useEntityProp(
	'root',
	'navigationArea',
	'navigation',
	navigationArea
	);

This won't work when the block is used in WP 5.9 without the Gutenberg plugin active as that REST API endpoint does not exist.

Step-by-step reproduction instructions

1. Run the latest WP 5.9 trunk with no Gutenberg plugin active.
2. Open the site editor.
3. Insert a Navigation block if there isn't already one on the page.
4. Open DevTools and look in the console.
5. You'll see a 404 error from a request to /wp/v2/block-navigation-areas.

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[talldan]

Could be tricky to solve. I think the original intent was to keep nav areas in the Gutenberg plugin until the deprecation period ends (not sure when that is and it might have already passed).

[noisysocks]

If it hasn't already passed then we could wrap the relevant bits of JavaScript with an if ( process.env.GUTENBERG_PHASE === 2 ).