Small refactoring + Re-assign the sanitized/transliterated filename to $_FILES array

[exside]

What does it do?

• Refactors how the filename is transliterated, moved away from creating a new modResource object to calling the method of the modResource class via $modx->call().
• Re-assigns the sanitized/transliterated filename to the $_FILES array to not conflict with other extras also operating on filenames (like ContentBlocks for example)

  Why is it needed?

• The refactoring part makes it probably a bit faster (not sure, seems more elegant though) because no new (unnecessary) modResource object is created.
• The re-assigning part ensures compatibility with extras that also operate on filenames