is_building_sellable()
Introduce is_building_sellable(). Use it instead of is_wonder() to determine if a building must have zero upkeep. No functional changes, as initial version of is_building_sellable() returns values equivalent to old rules.
This is first step towards #42993
Introduce is_building_sellable(). Use it instead of is_wonder() to determine if a building must have zero upkeep. No functional changes, as initial version of is_building_sellable() returns values equivalent to old rules.
This is first step towards #42993