Fix item EAR ticks

Item entities only have their gravity ticked every 4 ticks when on ground.
Fix that and also remove Spigot's arbitrary tick skipping. It's a terribly
cheap way of getting extra performance that doesn't really work at all.

paper-server/patches/sources/net/minecraft/world/entity/item/ItemEntity.java.patch

@@ -84,6 +84,15 @@
  
              this.xo = this.getX();
              this.yo = this.getY();
+@@ -162,7 +175,7 @@
+                 }
+             }
+ 
+-            if (!this.onGround() || this.getDeltaMovement().horizontalDistanceSqr() > 9.999999747378752E-6D || (this.tickCount + this.getId()) % 4 == 0) {
++            if (!this.onGround() || this.getDeltaMovement().horizontalDistanceSqr() > 9.999999747378752E-6D || (this.tickCount + this.getId()) % 4 == 0) { // Paper - Diff on change; ActivationRange immunity
+                 this.move(MoverType.SELF, this.getDeltaMovement());
+                 this.applyEffectsFromBlocks();
+                 float f = 0.98F;
 @@ -188,9 +201,11 @@
                  this.mergeWithNeighbours();
              }

paper-server/src/main/java/org/spigotmc/ActivationRange.java

@@ -234,7 +234,7 @@ public class ActivationRange
     public static boolean checkIfActive(Entity entity)
     {
         // Never safe to skip fireworks or item gravity
-        if (entity instanceof FireworkRocketEntity || (entity instanceof ItemEntity && (entity.tickCount + entity.getId() + 1) % 4 == 0)) {
+        if (entity instanceof FireworkRocketEntity || (entity instanceof ItemEntity && (entity.tickCount + entity.getId()) % 4 == 0)) { // Paper - Needed for item gravity, see ItemEntity tick
             return true;
         }
 
@@ -253,11 +253,8 @@ public class ActivationRange
                 }
                 isActive = true;
             }
-            // Add a little performance juice to active entities. Skip 1/4 if not immune.
-        } else if ( !entity.defaultActivationState && entity.tickCount % 4 == 0 && !ActivationRange.checkEntityImmunities( entity ) )
-        {
-            isActive = false;
         }
+        // Paper - remove dumb tick skipping for active entities
         return isActive;
     }
 }