Merge pull request #15818 from colemanw/fields

Field metadata cleanup: Contact & Activity & Custom

diff --cc CRM/Activity/BAO/Activity.php
Simple merge

diff --cc CRM/Activity/DAO/Activity.php
Simple merge

diff --cc CRM/Contact/DAO/Contact.php
Simple merge

diff --cc Civi/Api4/Generic/DAOGetFieldsAction.php
Simple merge

diff --cc Civi/Api4/Service/Spec/FieldSpec.php
Simple merge

diff --cc Civi/Api4/Service/Spec/SpecFormatter.php
Simple merge

diff --cc Civi/Api4/Service/Spec/SpecGatherer.php
Simple merge