[6.x] Fix method and remove duplication

[shadoWalker89]

The tweak made by taylor on the on the FileFactory::create() has two problems

1- Using file_put_contents() on a resource this causes the following problem
ErrorException : file_put_contents() expects parameter 1 to be a valid path, resource given

2- Second one using the $tmp inside the closure without passing it via use() this will cause an undefined variable error.

Instead of applying fixes to these two problems i restaured the original code of the create() method plus checking if the $kilobytes is a string, if so i'll just call the createWithContent() instead