make adding newlines with to text more consistent and opt-out-able (#14158)

# Description

This PR tries to make `to text` more consistent with how it adds
newlines and also gives you an opt-out --no-newline option.

![image](https://github.com/user-attachments/assets/e4976ce6-c685-47a4-8470-4947970daf47)


I wasn't sure how to change the `PipelineData::ByteStream` match arm. I
figure something needs to be done there but I'm not sure how to do it.


# User-Facing Changes
newlines are more consistent.

# Tests + Formatting
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crates/nu-command/tests/commands/save.rs

@@ -415,7 +415,7 @@ fn save_with_custom_converter() {
 
         nu!(cwd: dirs.test(), pipeline(
             r#"
-                def "to ndjson" []: any -> string { each { to json --raw } | to text } ;
+                def "to ndjson" []: any -> string { each { to json --raw } | to text --no-newline } ;
                 {a: 1, b: 2} | save test.ndjson
             "#
         ));