DataMapper: Indent abstract wrapper field

[igarashitm]

Describe the Bug

Probably because abstract wrapper field is not draggable thus not showing draggable icon, it looks like shifting backwards (i.e. left). It would be better to have a blank space there.

Steps to Reproduce the Bug or Issue

1. Attach FIXML schema files - https://www.fixtrading.org/standards/fixml/

Screenshots or Videos

No response

Platform

• OS: [e.g. macOS, Windows, Linux]
• Browser: [e.g. Chrome, Safari, Firefox]
• Version: [e.g. 0.30.0]