Data generation for TypePassthrough should consider numeric values

[ohader]

• https://github.com/TYPO3/styleguide/blob/master/Classes/TcaDataGenerator/FieldGenerator/TypePassthrough.php
• https://docs.typo3.org/typo3cms/TCAReference/ColumnsConfig/Type/Passthrough.html

Using string values (currently) is just guessing something. The type of default property should be considered here. In case default is not defined, no value should be generated.