Fix form style bug in form builder

[RuthShryock]

Checklist

1. If you've added code that should be tested, add tests
2. If you've changed APIs, update (or create!) the documentation
3. Ensure the tests pass
4. Make sure that your code lints and that you've followed our coding style
5. Write a title and, if necessary, a description of your work suitable for publishing in our release notes
6. Mention any related issues in this repository (as #ISSUE) and in other repositories (as kobotoolbox/other#ISSUE)
7. Open an issue in the docs if there are UI/UX changes

Description

Allow form style setting to be retained when the user enters and leaves the form builder.

Notes

Changed the location of where we are accessing the settings__style variable when we open the form editor. The bug was that we were looking in the asset.settings_style which is undefined. The correct location is in the asset.content.settings.style.

Related issues

Fixes #3887

[notion-workspace]

Form builder bug