JS: missing implementations for imported C functions `rename`, `realpath` and `getcwd`, used in building `jsaddle-dom`

The following C functions are imported by various boot libraries, and in turn used by jsaddle-dom's Setup.hs script. Each missing JavaScript implementation can be made trivially with equivalent NodeJS functions:

• rename: imported by unix, equivalent to node's fs.renameSync
• realpath: imported by directory, equivalent to node's fs.realpathSync
• getcwd: imported by unix, equivalent to node's process.cwd