Issue with focus when created in a new window.

If a new window is created using `window.open()` and then the json editor is created with `target` property set to `wind.document.body` where `wind` is the new window or any other element inside `wind`, the editor stops functioning as usual. There seems to be some issue with focusing on the right element. E.g. the text field for key is not focused when a new prop is created.

[Link to pen demonstrating this behavior](https://codepen.io/kharon4/pen/VwQdGqg?editors=1000)

Reproduce the behavior with the linked CodePen: open a window with window.open(), create the JSON editor with target set to the new window's document.body or an element inside it, and create a new property. Trace the focus handling around the target property; done means the key text field receives focus as it does in the main window.

Written by the indexing model from the issue text.