Remove rowStyle reference and replace it by new RegisteredStyle class

src/Spout/Writer/Common/Manager/RegisteredStyle.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace Box\Spout\Writer\Common\Manager;
+
+use Box\Spout\Common\Entity\Style\Style;
+
+class RegisteredStyle
+{
+    /**
+     * @var Style
+     */
+    private $style;
+
+    /**
+     * @var bool
+     */
+    private $isRowStyle;
+
+    public function __construct(Style $style, bool $isRowStyle)
+    {
+        $this->style = $style;
+        $this->isRowStyle = $isRowStyle;
+    }
+
+    public function getStyle() : Style
+    {
+        return $this->style;
+    }
+
+    public function isRowStyle() : bool
+    {
+        return $this->isRowStyle;
+    }
+}