repl: Replace REPL panel with sessions view (#14981)

This PR removes the REPL panel and replaces it with a new sessions view
that gets displayed in its own pane.

The sessions view can be opened with the `repl: sessions` command (we
can adjust the name, as needed).

There was a rather in-depth refactoring needed to extricate the various
REPL functionality on the editor from the `RuntimePanel`.

<img width="1136" alt="Screenshot 2024-07-22 at 4 12 12 PM"
src="https://github.com/user-attachments/assets/ac0da351-778e-4200-b08c-39f9e77d78bf">

<img width="1136" alt="Screenshot 2024-07-22 at 4 12 17 PM"
src="https://github.com/user-attachments/assets/6ca53476-6ac4-4f8b-afc8-f7863f7065c7">

Release Notes:

- N/A

crates/repl/src/repl_store.rs

@@ -28,6 +28,10 @@ impl ReplStore {
     pub(crate) fn init(fs: Arc<dyn Fs>, cx: &mut AppContext) {
         let store = cx.new_model(move |cx| Self::new(fs, cx));
 
+        store
+            .update(cx, |store, cx| store.refresh_kernelspecs(cx))
+            .detach_and_log_err(cx);
+
         cx.set_global(GlobalReplStore(store))
     }
 
@@ -49,6 +53,10 @@ impl ReplStore {
         }
     }
 
+    pub fn fs(&self) -> &Arc<dyn Fs> {
+        &self.fs
+    }
+
     pub fn is_enabled(&self) -> bool {
         self.enabled
     }