Cache territory claiming base types
E.g. borders.c does several extra_type_by_cause_iterate(EC_BASE ...) iterations where it only cares about territory claiming bases. We should have cached list containing only territory claiming bases.
E.g. borders.c does several extra_type_by_cause_iterate(EC_BASE ...) iterations where it only cares about territory claiming bases. We should have cached list containing only territory claiming bases.