Add background color support for text boxes for Word writer

Author: hazington

src/PhpWord/Writer/Word2007/Element/TextBox.php

@@ -50,6 +50,9 @@ public function write(): void
         $xmlWriter->startElement('v:shape');
         $xmlWriter->writeAttribute('type', '#_x0000_t0202');
 
+        if ($style->getBgColor()) {
+            $xmlWriter->writeAttribute('fillcolor', $style->getBgColor());
+        }
         $styleWriter->write();
         $styleWriter->writeBorder();