Fix XLSX Writer on Windows plaftorms

A bug was introduced, preventing Spout to create valid XLSX files on Windows.
This commits reverts the changes that introduced DIRECTORY_SEPARATOR everywhere
and fixes the original issue with the writer by normalizing paths when creating
the zipped file.

src/Spout/Reader/Helper/XLSX/SharedStringsHelper.php

@@ -162,12 +162,11 @@ class SharedStringsHelper
     }
 
     /**
-     * @return string The path to the shared strings XML file, working cross-platforms
+     * @return string The path to the shared strings XML file
      */
     protected function getSharedStringsFilePath()
     {
-        $sharedStringsXmlFilePath = str_replace('/', DIRECTORY_SEPARATOR, self::SHARED_STRINGS_XML_FILE_PATH);
-        return 'zip://' . $this->filePath . '#' . $sharedStringsXmlFilePath;
+        return 'zip://' . $this->filePath . '#' . self::SHARED_STRINGS_XML_FILE_PATH;
     }
 
     /**
@@ -250,7 +249,7 @@ class SharedStringsHelper
     protected function getSharedStringTempFilePath($sharedStringIndex)
     {
         $numTempFile = intval($sharedStringIndex / self::MAX_NUM_STRINGS_PER_TEMP_FILE);
-        return $this->tempFolder . DIRECTORY_SEPARATOR . 'sharedstrings' . $numTempFile;
+        return $this->tempFolder . '/sharedstrings' . $numTempFile;
     }
 
     /**

src/Spout/Reader/Helper/XLSX/WorksheetHelper.php

@@ -186,8 +186,7 @@ class WorksheetHelper
      */
     protected function getFileAsXMLElementWithNamespace($xmlFilePath, $mainNamespace)
     {
-        $normalizedXmlFilePath = str_replace('/', DIRECTORY_SEPARATOR, $xmlFilePath);
-        $xmlContents = $this->globalFunctionsHelper->file_get_contents('zip://' . $this->filePath . '#' . $normalizedXmlFilePath);
+        $xmlContents = $this->globalFunctionsHelper->file_get_contents('zip://' . $this->filePath . '#' . $xmlFilePath);
 
         $xmlElement = new \SimpleXMLElement($xmlContents);
         $xmlElement->registerXPathNamespace('ns', $mainNamespace);

src/Spout/Reader/Internal/XLSX/Worksheet.php

@@ -33,12 +33,11 @@ class Worksheet
 
     /**
      * @return string Path of the XML file containing the worksheet data,
-     *                without the leading slash and working cross-platforms.
+     *                without the leading slash.
      */
     public function getDataXmlFilePath()
     {
-        $dataXmlFilePath = ltrim($this->dataXmlFilePath, '/');
-        return str_replace('/', DIRECTORY_SEPARATOR, $dataXmlFilePath);
+        return ltrim($this->dataXmlFilePath, '/');
     }
 
     /**