Dial in the channel creating/renaming UI

* Ensure channel list is in a consistent state with no flicker while the
  channel creation / rename request is outstanding.
* Maintain selection properly when renaming and creating channels.
* Style the channel name editor more consistently with the non-editable
  channel names.

Co-authored-by: Mikayla <mikayla@zed.dev>

crates/collab/src/tests.rs

@@ -278,8 +278,8 @@ impl TestServer {
         let channel_id = admin_client
             .app_state
             .channel_store
-            .update(admin_cx, |channel_store, _| {
-                channel_store.create_channel(channel, None)
+            .update(admin_cx, |channel_store, cx| {
+                channel_store.create_channel(channel, None, cx)
             })
             .await
             .unwrap();