fs: Change the default value of `mode` argument of `fs.copyFile()` to `fs.constants.COPYFILE_FICLONE`

### What is the problem this feature will solve? Today's operating systems and some file systems supports [copy-on-write operation](https://en.wikipedia.org/wiki/Copy-on-write#In_computer_storage) for copying a file (e.g. btrfs on Linux, APFS on Apple's Darwins). `fs.copyFile()` has already supported them as opt-in behavior if the underlying platform support such operations and libuv support them. - https://nodejs.org/api/fs.html#fspromisescopyfilesrc-dest-mode - https://github.com/libuv/libuv/blob/3f331e97da5b1cc2e24765dcb6d26c9dd313418f/src/unix/fs.c#L1309-L1490 However, it's still **opt-in** behavior. The default value of `mode` argument. of `fs.copyFile()` is `0`. This mean that `fs.copyFile()` does not use copy-on-write and use traditional copying mechanism operation even if the underlying platform and libuv supports such operation. An user can use copy-on-write operation by passing`fs.constants.COPYFILE_FICLONE` to `mode` argument. But if we forget to pass it, `fs.copyFile()` does not use an enhancement underlying mechanism. We (all programmers) tend to forget to supply a such optional flag to API and to lose a chance to improve a performance. I think this is a bug for API egonomics and having a value we should fix. ### What is the feature you are proposing to solve the problem? My proposal is changing the default value of `mode` argument of `fs.copyFile()` to `fs.constants.COPYFILE_FICLONE` from `0`. By this change, all exist programs using `fs.copyFile()` in all over the world can get a chance to improve their throughput without any code change. If the underlying platform does not support copy-on-write behavior, then `fs.constants.COPYFILE_FICLONE` flag fallback into the traditional approach. I think this change is painless approach. > `fs.constants.COPYFILE_FICLONE`: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then a fallback copy mechanism is used. > > https://nodejs.org/api/fs.html#f…