Great Wall(or other unique improvements)can buildt anywhere

After unlocking the Great Wall(No matter how you unlock it), you can build it anywhere. At that time, the default improvements of mountains, natural wonders, and oceans will become the following improvements. age-antiquity： Han great wall age-exploration： Ming great wall age-modern： STEPWELL If unlocking can be built on resources, I will not be able to obtain resources and empire resources will not be effective, so I did not unlock them. If you want to switch to other unique improvements, please replace the Great Wall in the code with the improvement you want( Only one unique improvement can be effective at the same time )