AutoLink port from Outer Rim (#10967)

* C# half of Outer Rim commit 5081906bd17e715ecae422dd7a003d9f103e6884 "autolink gaming."

Ported from Outer Rim with permission.

* YAML half of Outer Rim commit 5081906bd17e715ecae422dd7a003d9f103e6884 "autolink gaming."

Ported from Outer Rim with permission.

* commit fixed AL summary

Co-authored-by: Moony <moonheart08@users.noreply.github.com>

* NewLinkEvent.User & LinkAttemptEvent.User now nullable, fix possible AccessReaderSystem AutoLink bug

Co-authored-by: Moony <moonheart08@users.noreply.github.com>

Content.Server/MachineLinking/System/AutoLinkSystem.cs

@@ -0,0 +1,36 @@
+using Content.Server.MachineLinking.Components;
+
+namespace Content.Server.MachineLinking.System;
+
+/// <summary>
+/// This handles automatically linking autolinked entities at round-start.
+/// </summary>
+public sealed class AutoLinkSystem : EntitySystem
+{
+    [Dependency] private readonly SignalLinkerSystem _signalLinkerSystem = default!;
+
+    /// <inheritdoc/>
+    public override void Initialize()
+    {
+        SubscribeLocalEvent<AutoLinkTransmitterComponent, MapInitEvent>(OnAutoLinkMapInit);
+    }
+
+    private void OnAutoLinkMapInit(EntityUid uid, AutoLinkTransmitterComponent component, MapInitEvent args)
+    {
+        var xform = Transform(uid);
+
+        foreach (var receiver in EntityQuery<AutoLinkReceiverComponent>())
+        {
+            if (receiver.AutoLinkChannel != component.AutoLinkChannel)
+                continue; // Not ours.
+
+            var rxXform = Transform(receiver.Owner);
+
+            if (rxXform.GridUid != xform.GridUid)
+                continue;
+
+            _signalLinkerSystem.TryLinkDefaults(receiver.Owner, uid, null);
+        }
+    }
+}
+