[NUI] Add multi-mimetype feature for Drag and Drop (#6294)

[NUI] Add multi-mimetype feature for Drag and Drop (#6294)

* [NUI] Add multi-mimetype feature for Drag and Drop
Contents
- Allow to set multi-mimetypes for source client (use DragInfo)
- Target client receive source's mimetypes from source client when Enter, Move, Leave
- Target client can set mimetype to receive - Refactoring code for readability
- Refactoring codes for readability

* Refactoring data structure and duplicated codes

* Apply clean code for Drag and Drop