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/0618-fix-various-menus-with-empty-level-accesses.patch

@@ -0,0 +1,23 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Jake Potrebic <jake.m.potrebic@gmail.com>
+Date: Sun, 11 Jul 2021 12:52:56 -0700
+Subject: [PATCH] fix various menus with empty level accesses
+
+
+diff --git a/src/main/java/net/minecraft/world/inventory/ContainerLevelAccess.java b/src/main/java/net/minecraft/world/inventory/ContainerLevelAccess.java
+index c96b04f045dda384cdee9254a1765ef97e5f7f03..85e336637db8643fc5aca1dba724c9b341cbf46f 100644
+--- a/src/main/java/net/minecraft/world/inventory/ContainerLevelAccess.java
++++ b/src/main/java/net/minecraft/world/inventory/ContainerLevelAccess.java
+@@ -27,6 +27,12 @@ public interface ContainerLevelAccess {
+         public <T> Optional<T> evaluate(BiFunction<Level, BlockPos, T> getter) {
+             return Optional.empty();
+         }
++        // Paper start - fix menus with empty level accesses
++        @Override
++        public org.bukkit.Location getLocation() {
++            return null;
++        }
++        // Paper end - fix menus with empty level accesses
+     };
+ 
+     static ContainerLevelAccess create(final Level world, final BlockPos pos) {