NamespaceStringOrUUID::dbName() returns the dbName either that's on the NamespaceString or that's stored on NamespaceStringOrUUID itself. There isn't any need for NamespaceStringOrUUID::dbname(), and it's confusing to have so many methods that return the db name.

The function is only used in about 10 places, all of which can be converted to using db() instead. We'll need to change the code that generates the _dbName member for IDL defined command types here - we can just call NamespaceStringOrUUID::db().toString() here as well, the code that exists currently is essentially the same behavior as NamespaceStringOrUUID::db().