Re-add MultiWorkspace (#48800)

Release Notes:

- Added agent panel restoration. Now restarting your editor won't cause
your thread to be forgotten.

---------

Co-authored-by: Anthony Eid <56899983+Anthony-Eid@users.noreply.github.com>
Co-authored-by: Eric Holk <eric@zed.dev>
Co-authored-by: Danilo Leal <67129314+danilo-leal@users.noreply.github.com>
Co-authored-by: Anthony Eid <anthony@zed.dev>
Co-authored-by: Mikayla Maki <mikayla.c.maki@gmail.com>
Co-authored-by: Cameron Mcloughlin <cameron.studdstreet@gmail.com>

crates/git_ui/src/commit_view.rs

@@ -774,7 +774,7 @@ impl CommitView {
                 callback(repo, &sha, stash, commit_view_entity, workspace_weak, cx).await?;
                 anyhow::Ok(())
             })
-            .detach_and_notify_err(window, cx);
+            .detach_and_notify_err(workspace.weak_handle(), window, cx);
     }
 
     async fn close_commit_view(