feat(stdlib)!: Handle printing of reference cycles

[alex-snezhko]

Closes #1841

I used a style of reporting cycles similar to Node.js where references are labeled with numbers whenever there is a cycle. For example:

record A {
  val: Number,
  mut next: Option<A>
}

let a = { val: 1, next: None }
let aOpt = Some(a)
a.next = aOpt
print(a)

// output:
<1>: {
  val: 1,
  next: Some(<cycle to <1>>)
}

[spotandjake]

This looks awesome.

[ospencer]

Were you able to look into only allocating the vec if needed? If not, it'd probably be worth it to just allocate a vec and reuse it instead of making a new one each time.

[peblair]

LGTM, but see @ospencer's comment

[alex-snezhko]

@ospencer I did end up doing something like that; initially the allocated vector box is empty and then the first time that vecPush is called it initializes the vector (though you still have to allocate the vector box each time). Reusing one vector through every call to print sounds like an interesting idea, though (and maybe I'm thinking too far ahead here) would this continue to work properly with async/parallelism gets implemented and you are trying to print in multiple threads?

[ospencer]

I gotcha. We can decide to do that later as a further optimization. And yeah, it could cause some trouble for parallelism.