canWithdraw() + changes to displayable() (#6902)

* `shouldDiplay()` + `canWithdraw()`

* Better implementation of `displayable()`

core/src/mindustry/entities/comp/BuildingComp.java

@@ -613,6 +613,10 @@ abstract class BuildingComp implements Posc, Teamc, Healthc, Buildingc, Timerc,
         Fx.unitDrop.at(unit);
     }
 
+    public boolean canWithdraw(){
+        return true;
+    }
+
     public boolean canUnload(){
         return block.unloadable;
     }
@@ -1342,11 +1346,6 @@ abstract class BuildingComp implements Posc, Teamc, Healthc, Buildingc, Timerc,
     public ItemModule flowItems(){
         return items;
     }
-
-    public boolean displayable(){
-        return true;
-    }
-
     @Override
     public void display(Table table){
         //display the block stuff