Add native block-editor support

• Add wp-scripts for build
• Enqueue script, excluding it from widget block editor
• Localize script with configurable/filterable options
• Localize script with titles for post types to match current functionality
• Register meta and set sanitization callbacks
• Allow meta to be accessed via endpoint
• Create sidebar plugin to show the two fields used by the plugin

tests/bootstrap.php

@@ -5,9 +5,11 @@
  * @package External_Permalinks_Redux
  */
 
+// phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedVariableFound
 $_tests_dir = getenv( 'WP_TESTS_DIR' );
 
 if ( ! $_tests_dir ) {
+	// phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedVariableFound
 	$_tests_dir = rtrim( sys_get_temp_dir(), '/\\' ) . '/wordpress-tests-lib';
 }
 
@@ -22,10 +24,10 @@ require_once $_tests_dir . '/includes/functions.php';
 /**
  * Manually load the plugin being tested.
  */
-function _manually_load_plugin() {
+function epr__manually_load_plugin() {
 	require dirname( dirname( __FILE__ ) ) . '/external-permalinks-redux.php';
 }
-tests_add_filter( 'muplugins_loaded', '_manually_load_plugin' );
+tests_add_filter( 'muplugins_loaded', 'epr__manually_load_plugin' );
 
 // Start up the WP testing environment.
 require $_tests_dir . '/includes/bootstrap.php';