fixed broken movable TEs under Java 16

src/main/java/carpet/mixins/BlockEntity_movableBEMixin.java

@@ -1,13 +1,21 @@
 package carpet.mixins;
 
+import carpet.fakes.BlockEntityInterface;
 import net.minecraft.block.entity.BlockEntity;
 import net.minecraft.util.math.BlockPos;
+import org.spongepowered.asm.mixin.Final;
 import org.spongepowered.asm.mixin.Mixin;
-import org.spongepowered.asm.mixin.gen.Accessor;
+import org.spongepowered.asm.mixin.Mutable;
+import org.spongepowered.asm.mixin.Shadow;
 
 @Mixin(BlockEntity.class)
-public interface BlockEntity_movableBEMixin
+public abstract class BlockEntity_movableBEMixin implements BlockEntityInterface
 {
-    @Accessor
-    void setPos(BlockPos pos);
+    @Mutable
+    @Shadow @Final protected BlockPos pos;
+
+    public void setCMPos(BlockPos newPos)
+    {
+        pos = newPos;
+    };
 }