Fix #18908: Add stdClass as possible return type to getBodyParams (#18918)

framework/web/Request.php

@@ -554,7 +554,7 @@ class Request extends \yii\base\Request
      * Request parameters are determined using the parsers configured in [[parsers]] property.
      * If no parsers are configured for the current [[contentType]] it uses the PHP function `mb_parse_str()`
      * to parse the [[rawBody|request body]].
-     * @return array the request parameters given in the request body.
+     * @return array|object the request parameters given in the request body.
      * @throws \yii\base\InvalidConfigException if a registered parser does not implement the [[RequestParserInterface]].
      * @see getMethod()
      * @see getBodyParam()