[php-src] Issue #21114: SplFileInfo has no method isWriteable()

Issue: https://github.com/php/php-src/issues/21114
Author: JamesOlvertone

From manual page: https://php.net/class.recursivedirectoryiterator

---
The SplFileInfo Object has no isWriteable()-method:

$rdi = new RecursiveDirectoryIterator(__DIR__, FilesystemIterator::SKIP_DOTS);
$rit = new RecursiveIteratorIterator($rdi);

foreach ($rit as $fileinfo) {
  //fileinfo  is SplFileInfo-Object

  echo $fileinfo . ":" . PHP_EOL;

  $fileinfo->isDir();              // this method exists
  $fileinfo->isReadable();    // this too
  is_writeable($fileinfo);     // this works

  // error: PHP Fatal error:  
  //Uncaught Error: Call to undefined method SplFileInfo::isWriteable() 
  $fileinfo->isWriteable();   
}