Make to text stream ListStreams (#7577)

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.

crates/nu-command/tests/commands/mod.rs

@@ -90,6 +90,7 @@ mod split_row;
 mod str_;
 mod table;
 mod take;
+mod to_text;
 mod touch;
 mod transpose;
 mod try_;