MDL-62315 form: Implement the privacy API for core_form subsystem
Forms subsystem has no own database table. The only personal data is the
user preference 'filemanager_recentviewmode' that stores the view mode
of the file picker element.
It was discussed whether handling of this preference should be added
here into core_form, or rather into core_repository subsystem. The final
decision was to consider the preference as owned by the core_form
because it is affecting the display of a form element, not the
repository backend (even though the strings describing it had been put
into core_repository strings).