Use PHP 7.4 featers and PHP 8 polyfills

rector.php

@@ -0,0 +1,26 @@
+<?php
+declare(strict_types=1);
+
+use Rector\Config\RectorConfig;
+use Rector\TypeDeclaration\Rector\ClassMethod\AddVoidReturnTypeWhereNoReturnRector;
+return RectorConfig::configure()
+	->withPaths(
+		[
+			__DIR__ . '/inc',
+			__DIR__ . '/views',
+		]
+	)
+	->withAutoloadPaths(
+		[
+			__DIR__ . '/vendor/squizlabs/php_codesniffer/autoload.php',
+			__DIR__ . '/vendor/php-stubs/wordpress-stubs/wordpress-stubs.php',
+		]
+	)
+	->withSkipPath(__DIR__ . '/vendor',)
+	->withImportNames(false)
+	->withPhpSets()
+	->withRules(
+		[
+			AddVoidReturnTypeWhereNoReturnRector::class,
+		]
+	);