Add serialize metadata to tag used_for field

[colemanw]

Overview

Add schema metadata to the Tag "used_for" field, which is a comma separated list.

Before

Less metadata.

After

More metadata

[civibot]

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[eileenmcnaughton]

@colemanw the syntaxconformance test might need to be smarter about what data to put in that field to pass

[colemanw]

So Eileen, according to the test failure, the testCreateSingleValueAlter() function is setting the field's value to 5 which is actually the constant CRM_Core_DAO::SERIALIZE_COMMA. This is due to this line of code which doesn't make sense to me - it is actually setting the value of $field['serialize'] (in this case 5) as the value of the field:

https://github.com/civicrm/civicrm-core/blob/5.13/tests/phpunit/api/v3/SyntaxConformanceTest.php#L1502-L1504

  if (!empty($specs['serialize'])) {
    $updateParams[$field] = $entity[$field] = (array) $specs['serialize'];
  }

[colemanw]

Ok removing those lines fixed the test.