Integrate with the File System Access API as a progressive enhancement

[tomayac]

It would be great if this made use of DataTransferItem.getAsFileSystemHandle() from the File System Access API as a progressive enhancement as per my write-up. This way, dropped files could be edited right away (instead of forcing a download of a copy), which would be a great win for apps that need to modify dropped files, like online image editors. Also see the MDN docs.

[dreyescabrera]

Apparently this lib doesn't bother. That's sad since I want to adopt the new API.