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.

1 files changed, 18 insertions, 0 deletions

diff --git a/patches/server/0573-Config-option-for-Piglins-guarding-chests.patch b/patches/server/0573-Config-option-for-Piglins-guarding-chests.patch
new file mode 100644
index 0000000000..8e2094a53d
--- /dev/null
+++ b/patches/server/0573-Config-option-for-Piglins-guarding-chests.patch
@@ -0,0 +1,18 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Jason Penilla <[email protected]>
+Date: Wed, 2 Dec 2020 03:07:58 -0800
+Subject: [PATCH] Config option for Piglins guarding chests
+
+
+diff --git a/src/main/java/net/minecraft/world/entity/monster/piglin/PiglinAi.java b/src/main/java/net/minecraft/world/entity/monster/piglin/PiglinAi.java
+index 3ca643747535bf7b71e5877ca47f730a2aca4ba5..d601bff8e8f62af78791ad357b51b92faf04e55f 100644
+--- a/src/main/java/net/minecraft/world/entity/monster/piglin/PiglinAi.java
++++ b/src/main/java/net/minecraft/world/entity/monster/piglin/PiglinAi.java
+@@ -476,6 +476,7 @@ public class PiglinAi {
+     }
+ 
+     public static void angerNearbyPiglins(Player player, boolean blockOpen) {
++        if (!player.level().paperConfig().entities.behavior.piglinsGuardChests) return; // Paper - Config option for Piglins guarding chests
+         List<Piglin> list = player.level().getEntitiesOfClass(Piglin.class, player.getBoundingBox().inflate(16.0D));
+ 
+         list.stream().filter(PiglinAi::isIdle).filter((entitypiglin) -> {