fs.CopyFile should support copying metadata

[AkihiroSuda]

continuity/fs/copy.go

Lines 161 to 176 in 1805252

	// CopyFile copies the source file to the target.
	// The most efficient means of copying is used for the platform.
	func CopyFile(target, source string) error {
	src, err := os.Open(source)
	if err != nil {
	return errors.Wrapf(err, "failed to open source %s", source)
	}
	defer src.Close()
	tgt, err := os.Create(target)
	if err != nil {
	return errors.Wrapf(err, "failed to open target %s", target)
	}
	defer tgt.Close()
	return copyFileContent(tgt, src)
	}

The current implementation of CopyFile does not support copying metadata.
CopyFile should optionally copy the metadata as in CopyDir