Add ApiAdapter method to abstract some metadata default handling

[andyjefferson]

With JPA / Jakarta if using persistent properties and a property is not provided we should default to adding the property internally. With JDO this is the opposite. This logic is currently hardcoded into datanucleus-core metadata classes. We should abstract it out into ApiAdapter and just check on the appropriate method for what to do

Similarly with JPA / Jakarta we have a default mapping-file location for persistence.xml, namely "META-INF/orm.xml". JDO doesn't do this. We should abstract this into ApiAdapter also