Restore customizer

restore_customizer.php

<?php 
namespace utkarsh;
	
/**
 * Restore customizer which is removed by WP Core.
 */
function restore_customizer() {
	// WP version is 5.9 beta or later than only add customize.php back.
	if ( ! version_compare( get_bloginfo( 'version' ), '5.9-beta', '>=' ) ) {
		return;
	}
	// Add customize.php menu.
	add_submenu_page(
		'themes.php',
		__( 'Customize' ),
		__( 'Customize' ),
		'customize',
		'customize.php'
	);
}

/**
 * Restore customizer which is removed by gutenberg after full site editing.
 */
function restore_customizer_gutenberg() {
	// Following is for gutenberg plugin, Remove action has safe check.
	remove_action( 'admin_menu', 'gutenberg_remove_legacy_pages' );
}
add_action( 'init', __NAMESPACE__ . '\restore_customizer_gutenberg' );
add_action( 'admin_menu', __NAMESPACE__ . '\restore_customizer' );