Support fuse copy_file_range?

[labulakalia]

some link:
http://libfuse.github.io/doxygen/structfuse__operations.html#a8b68daa154f8400cfb76e790aad9e697
bazil/fuse#245

[stapelberg]

Not sure what that would involve, or how feasible it is.

More details or pull requests welcome (to then discuss and see if we can accept the change).