Gutenberg 6.5: Add Nonce Endpoint

[iseulde]

This is a follow up to #47843.
See https://core.trac.wordpress.org/ticket/47843#comment:29.

I added the action that was added for the plugin in ​https://github.com/WordPress/gutenberg/pull/16683.

This can be tested by adding lowering the nonce life to 5 seconds. Load the page, then wait 5 seconds and try to update or publish a post.

<?php

add_filter( 'nonce_life', function() {
        return 5;
} );

[iseulde]

When testing, it is good to look at the network requests. Whenever the nonce expires, the REST API will return 403. A new nonce will be requested with the new action, and the original request will be remade.

[iseulde]

Running the tests, then will commit. ​https://github.com/WordPress/wordpress-develop/pull/101

[iseulde]

In 46253:

Editor: Add Nonce Endpoint

This is a follow up to #47843, implementing a PHP endpoint and inline scripts
after the editor package updates. The action was originally added in
​https://github.com/WordPress/gutenberg/pull/16683.

Fixes #48076.