Registers the user meta property for persisted preferences.

This property is used to store user preferences across page reloads and is
currently used by the block editor for preferences like ‘fullscreenMode’ and
‘fixedToolbar’.

function wp_register_persisted_preferences_meta() {
	/*
	 * Create a meta key that incorporates the blog prefix so that each site
	 * on a multisite can have distinct user preferences.
	 */
	global $wpdb;
	$meta_key = $wpdb->get_blog_prefix() . 'persisted_preferences';

	register_meta(
		'user',
		$meta_key,
		array(
			'type'         => 'object',
			'single'       => true,
			'show_in_rest' => array(
				'name'   => 'persisted_preferences',
				'type'   => 'object',
				'schema' => array(
					'type'                 => 'object',
					'context'              => array( 'edit' ),
					'properties'           => array(
						'_modified' => array(
							'description' => __( 'The date and time the preferences were updated.' ),
							'type'        => 'string',
							'format'      => 'date-time',
							'readonly'    => false,
						),
					),
					'additionalProperties' => true,
				),
			),
		)
	);
}