This PR changes `to text` so that when given a `ListStream`, it streams
the incoming values instead of collecting them all first.
The easiest way to observe/verify this PR is to convert a list to a very
slow `ListStream` with `each`:
```bash
ls | get name | each {|n| sleep 1sec; $n} | to text
```
The `to text` output will appear 1 item at a time.
