Implement some BlockData stuff on Fabric, make stuff less jank

common/src/main/java/com/dfsek/terra/api/generic/world/block/data/Slab.java

@@ -1,4 +1,11 @@
 package com.dfsek.terra.api.generic.world.block.data;
 
-public interface Slab extends Bisected, Waterlogged {
+public interface Slab extends Waterlogged {
+    Type getType();
+
+    void setType(Type type);
+
+    enum Type {
+        TOP, BOTTOM, DOUBLE
+    }
 }