I'm not opposed to adding a method like this to the FileSystem API, but I don't think it should be added until it supports recursive directory copying to match `unlink`. I also think it should just be called `copy` instead of `copyItem`. 

If the underlying appshell copy function is not recursive, then in the meantime we could consider cleaning up `SpecRunnerUtils.copyPath`, moving it to `FileUtils` and using it from there. Having a native copy implementation would certainly be good to have, but also probably isn't a blocker for Brackets (desktop) features like this.