Remove wall-time / unused skip tick protection (#11412)

Spigot still maintains some partial implementation of "tick skipping", a
practice in which the MinecraftServer.currentTick field is updated not
by an increment of one per actual tick, but instead set to
System.currentTimeMillis() / 50. This behaviour means that the tracked
tick may "skip" a tick value in case a previous tick took more than the
expected 50ms.

To compensate for this in important paths, spigot/craftbukkit
implements "wall-time". Instead of incrementing/decrementing ticks on
block entities/entities by one for each call to their tick() method,
they instead increment/decrement important values, like
an ItemEntity's age or pickupDelay, by the difference of
`currentTick - lastTick`, where `lastTick` is the value of
`currentTick` during the last tick() call.

These "fixes" however do not play nicely with minecraft's simulation
distance as entities/block entities implementing the above behaviour
would "catch up" their values when moving from a non-ticking chunk to a
ticking one as their `lastTick` value remains stuck on the last tick in
a ticking chunk and hence lead to a large "catch up" once ticked again.

Paper completely removes the "tick skipping" behaviour (See patch
"Further-improve-server-tick-loop"), making the above precautions
completely unnecessary, which also rids paper of the previous described
incompatibility with non-ticking chunks.

patches/server/0399-Add-BellRingEvent.patch

@@ -0,0 +1,25 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Eearslya Sleiarion <eearslya@gmail.com>
+Date: Sun, 23 Aug 2020 13:04:02 +0200
+Subject: [PATCH] Add BellRingEvent
+
+Add a new event, BellRingEvent, to trigger whenever a player rings a
+village bell. Passes along the bell block and the player who rang it.
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java b/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java
+index f633d08b35bf9018367a449cc000c6c6ca5a44cd..dbe7931dd7eb43f9381463d3a57ba1eb53820985 100644
+--- a/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java
++++ b/src/main/java/org/bukkit/craftbukkit/event/CraftEventFactory.java
+@@ -378,10 +378,11 @@ public class CraftEventFactory {
+         return tradeSelectEvent;
+     }
+ 
++    @SuppressWarnings("deprecation") // Paper use deprecated event to maintain compat (it extends modern event)
+     public static boolean handleBellRingEvent(Level world, BlockPos position, Direction direction, Entity entity) {
+         Block block = CraftBlock.at(world, position);
+         BlockFace bukkitDirection = CraftBlock.notchToBlockFace(direction);
+-        BellRingEvent event = new BellRingEvent(block, bukkitDirection, (entity != null) ? entity.getBukkitEntity() : null);
++        BellRingEvent event = new io.papermc.paper.event.block.BellRingEvent(block, bukkitDirection, (entity != null) ? entity.getBukkitEntity() : null); // Paper - deprecated BellRingEvent
+         Bukkit.getPluginManager().callEvent(event);
+         return !event.isCancelled();
+     }