Make items float on water (#265)

Author: PetteriM1

src/main/java/cn/nukkit/entity/item/EntityItem.java

@@ -152,7 +152,13 @@ public boolean onUpdate(int currentTick) {
                 }
             }
 
-            this.motionY -= this.getGravity();
+            if (this.level.getBlockIdAt((int) this.x, (int) this.boundingBox.getMaxY(), (int) this.z) == 8 || this.level.getBlockIdAt((int) this.x, (int) this.boundingBox.getMaxY(), (int) this.z) == 9) { //item is fully in water or in still water
+                this.motionY -= this.getGravity() * -0.015;
+            } else if (this.isInsideOfWater()) {
+                this.motionY = this.getGravity() - 0.06; //item is going up in water, don't let it go back down too fast
+            } else {
+                this.motionY -= this.getGravity(); //item is not in water
+            }
 
             if (this.checkObstruction(this.x, this.y, this.z)) {
                 hasUpdate = true;