Use translation keys instead of hardcoded labels in layouts

When generating layouts in view designers, widget labels are hardcoded with the field name. A studio user must then change/fix all the labels manually in all layouts.

A very high value improvement would be to:

• use translation keys in the generated layouts (ex: label.schema_name.field_name)
• automatically populate messages.json with the translation keys from the previous step

This way, even if the application supports only one language, a label can be changed in the 4 layouts of a document in a single place.