trix-toolbar can't put after trix-editor

trix form can only works when `trix-toolbar` put before `trix-editor`

##### Steps to Reproduce

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When `trix-toolbar` put after `trix-editor`, I will get an error when submit the form.

```
An invalid form control with name='href' is not focusable.
```

I have to fix it by put the `trix-toolbar` before `trix-editor` like this:

```

```

##### Details

* Trix version: 1.3.1
* Browser name and version: Chrome 90
* Operating system: Mac OS 11.4