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

### 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
I think so, would have to check though, this method is used by cleanAlias() or how it's called, that's how I found it in the first place =)