ListStream touchup (#12524)

# Description

Does some misc changes to `ListStream`:
- Moves it into its own module/file separate from `RawStream`.
- `ListStream`s now have an associated `Span`.
- This required changes to `ListStreamInfo` in `nu-plugin`. Note sure if
this is a breaking change for the plugin protocol.
- Hides the internals of `ListStream` but also adds a few more methods.
- This includes two functions to more easily alter a stream (these take
a `ListStream` and return a `ListStream` instead of having to go through
the whole `into_pipeline_data(..)` route).
  -  `map`: takes a `FnMut(Value) -> Value`
  - `modify`: takes a function to modify the inner stream.

crates/nu-plugin-protocol/src/lib.rs

@@ -116,6 +116,7 @@ impl PipelineDataHeader {
 #[derive(Serialize, Deserialize, Debug, PartialEq, Eq, Clone)]
 pub struct ListStreamInfo {
     pub id: StreamId,
+    pub span: Span,
 }
 
 /// Additional information about external streams