Spring Improve consistency in StandardMultipartFile implementation

This PR refactors the StandardMultipartFile class to enhance consistency

Changes include:

1. Removed the transferTo(Path dest) method from StandardMultipartFile, as it is already provided as a default method in the MultipartFile interface.
2. Updated the transferTo(File dest) method to use getInputStream() for consistency with the MultipartFile interface's default transferTo(Path dest) implementation.
3. Modified the isEmpty and getBytes methods to also utilize internal methods (getSize() and getInputStream() respectively) for better code consistency.