Introduce native Gutenberg controls

• Register meta
• Enqueue script
• Switch to use_block_editor_for_post_type and remove the option
• Build component
• Add sanitize callback to handle special cases
• Add auth callback to allow "private" meta to be edited
• Add padding between modal buttons
• Don't hide UI if set to 0, as there's no way to update the setting
• Switch to @wordpress/scripts
• Consider moving Gutenberg bits, and/or REST API elements, to their own class.

inc/class-block-editor.php

@@ -34,19 +34,6 @@ class Block_Editor {
 		add_action( 'rest_api_init', array( $this, 'action_rest_api_init' ) );
 		add_filter( 'is_protected_meta', array( $this, 'filter_is_protected_meta' ), 10, 2 );
 		add_action( $this->cron_action, array( WP_Revisions_Control::get_instance(), 'do_purge_excess' ), 10, 2 );
-		add_action( 'admin_init', array( $this, 'action_admin_init' ) );
-	}
-
-	/**
-	 * Register admin-only hooks.
-	 *
-	 * @return void
-	 */
-	public function action_admin_init() {
-		if ( ! function_exists( 'use_block_editor_for_post' ) ) {
-			return;
-		}
-
 		add_action( 'enqueue_block_editor_assets', array( $this, 'action_enqueue_block_editor_assets' ) );
 	}