Synchronize access to Bukkit#createBlockData to prevent occasional ConcurrentModification exceptions

- This isn't actually used anymore given the previous commit, however it's still best to keep it safe.

worldedit-bukkit/src/main/java/com/sk89q/worldedit/bukkit/adapter/impl/FAWE_Spigot_v1_15_R2.java

@@ -144,7 +144,7 @@ public final class FAWE_Spigot_v1_15_R2 extends CachedBukkitAdapter implements I
     }
 
     @Override
-    public BlockMaterial getMaterial(BlockState state) {
+    public synchronized BlockMaterial getMaterial(BlockState state) {
         IBlockData bs = ((CraftBlockData) Bukkit.createBlockData(state.getAsString())).getState();
         return new BlockMaterial_1_15_2(bs.getBlock(), bs);
     }

worldedit-bukkit/src/main/java/com/sk89q/worldedit/bukkit/adapter/impl/FAWE_Spigot_v1_16_R1.java

@@ -144,7 +144,7 @@ public final class FAWE_Spigot_v1_16_R1 extends CachedBukkitAdapter implements I
     }
 
     @Override
-    public BlockMaterial getMaterial(BlockState state) {
+    public synchronized BlockMaterial getMaterial(BlockState state) {
         IBlockData bs = ((CraftBlockData) Bukkit.createBlockData(state.getAsString())).getState();
         return new BlockMaterial_1_16_1(bs.getBlock(), bs);
     }

worldedit-bukkit/src/main/java/com/sk89q/worldedit/bukkit/adapter/impl/FAWE_Spigot_v1_16_R2.java

@@ -146,7 +146,7 @@ public final class FAWE_Spigot_v1_16_R2 extends CachedBukkitAdapter implements I
     }
 
     @Override
-    public BlockMaterial getMaterial(BlockState state) {
+    public synchronized BlockMaterial getMaterial(BlockState state) {
         IBlockData bs = ((CraftBlockData) Bukkit.createBlockData(state.getAsString())).getState();
         return new BlockMaterial_1_16_2(bs.getBlock(), bs);
     }

worldedit-bukkit/src/main/java/com/sk89q/worldedit/bukkit/adapter/impl/FAWE_Spigot_v1_16_R3.java

@@ -146,7 +146,7 @@ public final class FAWE_Spigot_v1_16_R3 extends CachedBukkitAdapter implements I
     }
 
     @Override
-    public BlockMaterial getMaterial(BlockState state) {
+    public synchronized BlockMaterial getMaterial(BlockState state) {
         IBlockData bs = ((CraftBlockData) Bukkit.createBlockData(state.getAsString())).getState();
         return new BlockMaterial_1_16_4(bs.getBlock(), bs);
     }