REPL: Refactor output (#16927)

Shuffle `outputs.rs` into individual `outputs/*.rs` files and start
documenting them more.

Release Notes:

- N/A

crates/repl/src/session.rs

@@ -1,9 +1,9 @@
 use crate::components::KernelListItem;
+use crate::KernelStatus;
 use crate::{
     kernels::{Kernel, KernelSpecification, RunningKernel},
     outputs::{ExecutionStatus, ExecutionView},
 };
-use crate::{stdio, KernelStatus};
 use client::telemetry::Telemetry;
 use collections::{HashMap, HashSet};
 use editor::{
@@ -115,7 +115,7 @@ impl EditorBlock {
     ) -> RenderBlock {
         let render = move |cx: &mut BlockContext| {
             let execution_view = execution_view.clone();
-            let text_style = stdio::text_style(cx);
+            let text_style = crate::outputs::plain::text_style(cx);
 
             let gutter = cx.gutter_dimensions;