Editor toolbar configuration (#7338)

Adds settings for hiding breadcrumbs and quick action bar from
the editor toolbar. If both elements are hidden, the toolbar disappears
completely.

Example:

```json
"toolbar": {
  "breadcrumbs": true,
  "quick_actions": false
}
```

- It intentionally doesn't hide breadcrumbs in other views (for
instance, in the search result window) because their usage there differ
from the main editor.
- The editor controls how breadcrumbs are displayed in the toolbar, so
implementation differs a bit for breadcrumbs and quick actions bar.

Release Notes:

- Added support for configuring the editor toolbar ([4756](https://github.com/zed-industries/zed/issues/4756))

crates/zed/src/zed.rs

@@ -353,7 +353,7 @@ fn initialize_pane(workspace: &mut Workspace, pane: &View<Pane>, cx: &mut ViewCo
             toolbar.add_item(buffer_search_bar.clone(), cx);
 
             let quick_action_bar =
-                cx.new_view(|_| QuickActionBar::new(buffer_search_bar, workspace));
+                cx.new_view(|cx| QuickActionBar::new(buffer_search_bar, workspace, cx));
             toolbar.add_item(quick_action_bar, cx);
             let diagnostic_editor_controls = cx.new_view(|_| diagnostics::ToolbarControls::new());
             toolbar.add_item(diagnostic_editor_controls, cx);