Node: Adding missing fs methods + fixing a few method signatures

Added:
* `fs.readlinkSync`
* `fs.ftruncate`
* `fs.ftruncateSync`

Fixed:
* `process.cwd`
* `path.resolve`
* `fs.realpath`
* `fs.realpathSync`
* `fs.truncate`
* `fs.truncateSync`