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/0424-Add-getOfflinePlayerIfCached-String.patch

@@ -0,0 +1,39 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: oxygencraft <21054297+oxygencraft@users.noreply.github.com>
+Date: Sun, 25 Oct 2020 18:34:50 +1100
+Subject: [PATCH] Add getOfflinePlayerIfCached(String)
+
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+index 0b288cc080869efed42a28be682f7b68f8691416..ae594610d1c5665aa142522a9cbb97cf6e4d10f2 100644
+--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
++++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+@@ -1963,6 +1963,28 @@ public final class CraftServer implements Server {
+         return result;
+     }
+ 
++    // Paper start
++    @Override
++    @Nullable
++    public OfflinePlayer getOfflinePlayerIfCached(String name) {
++        Preconditions.checkArgument(name != null, "Name cannot be null");
++        Preconditions.checkArgument(!name.isEmpty(), "Name cannot be empty");
++
++        OfflinePlayer result = getPlayerExact(name);
++        if (result == null) {
++            GameProfile profile = console.getProfileCache().getProfileIfCached(name);
++
++            if (profile != null) {
++                result = getOfflinePlayer(profile);
++            }
++        } else {
++            offlinePlayers.remove(result.getUniqueId());
++        }
++
++        return result;
++    }
++    // Paper end
++
+     @Override
+     public OfflinePlayer getOfflinePlayer(UUID id) {
+         Preconditions.checkArgument(id != null, "UUID id cannot be null");