Start on adding support for editing via the assistant panel (#14795)

Note that this shouldn't have any visible user-facing behavior yet. The
feature is incomplete but we wanna merge early to avoid a long-running
branch.

Release Notes:

- N/A

---------

Co-authored-by: Nathan <nathan@zed.dev>

crates/command_palette/src/command_palette.rs

@@ -477,7 +477,7 @@ mod tests {
         });
 
         workspace.update(cx, |workspace, cx| {
-            workspace.add_item_to_active_pane(Box::new(editor.clone()), None, cx);
+            workspace.add_item_to_active_pane(Box::new(editor.clone()), None, true, cx);
             editor.update(cx, |editor, cx| editor.focus(cx))
         });