Indicate if a field is localized in UI

[denolfe]

Feature Request

Add visual indicator if a field is localized in the UI.

Detail

Currently, there is no way for an editor to know if a field is localized. This adds to uncertainty and possibly confusion when switching locales. Adding a visual indicator next to a field if it is localized would be a welcome change.

Example POC: #3160

[tylandavis]

Related #1308

[tylandavis]

This could be more useful if it shows the locale currently being edited.