Merge pull request #18347 from colemanw/fixSerializeLegacy

CRM/Core/DAO/CustomField.php

CRM/Upgrade/Incremental/sql/5.29.1.mysql.tpl

api/v3/CustomField.php

tests/phpunit/CRM/Core/BAO/CustomFieldTest.php

tests/phpunit/CRM/Core/BAO/CustomQueryTest.php

tests/phpunit/CRM/Utils/Migrate/fixtures/Activity-text.xml

...punit/CRM/Utils/Migrate/fixtures/ActivityMeeting-text.xml

tests/phpunit/CRM/Utils/Migrate/fixtures/Contact-text.xml

tests/phpunit/CRM/Utils/Migrate/fixtures/Individual-text.xml

...nit/CRM/Utils/Migrate/fixtures/IndividualStudent-text.xml

tests/phpunit/api/v3/CustomFieldTest.php

tests/phpunit/api/v4/Action/CustomValueTest.php

xml/schema/Core/CustomField.xml