implement block in hand

(cherry picked from commit 75fd4edd9f67b2cbf5abffc1ea417920106b1353)

src/js/net/minecraft/util/MetadataChunkBlock.js

@@ -33,7 +33,7 @@ window.MetadataChunkBlock = class {
                     let newLevel = 0;
                     let typeId = world.getBlockAt(x, y, z);
                     let block = Block.getById(typeId);
-                    let opacity = typeId === 0 ? 0 : block.getOpacity() * 255;
+                    let opacity = typeId === 0 ? 0 : Math.round(block.getOpacity() * 255);
 
                     if (opacity === 0) {
                         opacity = 1;

src/js/net/minecraft/util/Random.js

@@ -1,6 +1,8 @@
 window.Random = class {
 
-    constructor(seed) {
+    static instances = 0;
+
+    constructor(seed = Date.now() % 1000000000 ^ Random.instances++ * 1000) {
         this.mask = 0xffffffff;
         this.m_w = (123456789 + seed) & this.mask;
         this.m_z = (987654321 - seed) & this.mask;