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))