Error: Visual editing breaks image previews

**Describe the bug**

Currently, when `visualEditing` is enabled, all strings get stega-encoded in the preview. This breaks the image preview as lots of invisible characters get appended to the URL.

**Possible fixes**

Ideally, each widget could decide if and how its values should be encoded. Since we currently have no access to the widget, we could check the field type string and restrict the encoding to well-known core widgets (string/text/markdown) and allow string widgets to opt out on a per-field basis.

**What's next?**

I'll submit a PR with a simple fix.