Change the `CommandConstructor` type to just `Command` with factory methods, so that build commands and prebuild commands can be created. The actual enum values are an implementation detail — plugins use the factor methods, as they did with the command constructor.
Change the `CommandConstructor` type to just `Command` with factory methods, so that build commands and prebuild commands can be created. The actual enum values are an implementation detail — plugins use the factor methods, as they did with the command constructor.

abertelrud/swift-evolution,natecook1000/swift-evolution,apple/swift-evolution,apple/swift-evolution,natecook1000/swift-evolution,abertelrud/swift-evolution