Use Civi::entity()->getFields() for adding BAO fields to field spec

[jensschuppe]

See related TODOs:

• de.systopia.eck/Civi/Api4/Service/Spec/Provider/EckEntitySpecProvider.php

  Lines 27 to 34 in 602efd3

  	// TODO: Use `Civi::entity()->getFields()` instead
  	foreach ($bao::getSupportedFields() as $DAOField) {
  	if (NULL === $spec->getFieldByName($DAOField['name'])) {
  	$this->setDynamicFk($DAOField, $spec);
  	$field = self::arrayToField($DAOField, $entityName);
  	$spec->addFieldSpec($field);
  	}
  	}

• de.systopia.eck/Civi/Api4/Service/Spec/Provider/EckEntitySpecProvider.php

  Lines 44 to 50 in 602efd3

  	/**
  	* Copied from \Civi\Api4\Service\Spec\SpecFormatter
  	*
  	* TODO: Use `Civi::entity()->getFields()` instead of DAO::fields()
  	* so we don't need this copied function
  	*/
  	private static function arrayToField(array $data, string $entityName): FieldSpec {

and remove then unused code as well as the PHPStan baseline which is ignoring errors in that copied code.