Register stubs file for deepsource

Author: truongwp

composer.json

@@ -29,6 +29,11 @@
             "classes/views/"
 		]
 	},
+	"autoload-dev": {
+		"files": [
+			"stubs.php"
+		]
+	},
 	"require-dev": {
 		"php-stubs/wordpress-stubs": "^5.9",
 		"yoast/phpunit-polyfills": "^1.0",