Smalltalk: Node: FS: Implement full methods plus unit tests

For sync and async.
For promise APIs, not callback APIs (duplicate).
But convert all to callbacks in ST 'then: block error: errorBlock' to stop async method propagation.
For FileHandle class and global modulfe functions (somewhat duplicate).
(Gee, Node.js is a bit of a mess in this area :)

Also add full unit tests, of course.