Use ECS prototype-reload events (#22613)

* Use ECS prototype-reload events

* better constructors

* Maybe this fixes tests?

Content.Shared/Alert/AlertsSystem.cs

@@ -1,3 +1,4 @@
+using System.Collections.Frozen;
 using System.Diagnostics.CodeAnalysis;
 using Robust.Shared.Player;
 using Robust.Shared.Prototypes;
@@ -7,7 +8,8 @@ namespace Content.Shared.Alert;
 public abstract class AlertsSystem : EntitySystem
 {
     [Dependency] private readonly IPrototypeManager _prototypeManager = default!;
-    private readonly Dictionary<AlertType, AlertPrototype> _typeToAlert = new();
+
+    private FrozenDictionary<AlertType, AlertPrototype> _typeToAlert = default!;
 
     public IReadOnlyDictionary<AlertKey, AlertState>? GetActiveAlerts(EntityUid euid)
     {
@@ -170,9 +172,8 @@ public abstract class AlertsSystem : EntitySystem
         SubscribeLocalEvent<AlertsComponent, PlayerAttachedEvent>(OnPlayerAttached);
 
         SubscribeNetworkEvent<ClickAlertEvent>(HandleClickAlert);
-
+        SubscribeLocalEvent<PrototypesReloadedEventArgs>(HandlePrototypesReloaded);
         LoadPrototypes();
-        _prototypeManager.PrototypesReloaded += HandlePrototypesReloaded;
     }
 
     protected virtual void HandleComponentShutdown(EntityUid uid, AlertsComponent component, ComponentShutdown args)
@@ -185,29 +186,25 @@ public abstract class AlertsSystem : EntitySystem
         RaiseLocalEvent(uid, new AlertSyncEvent(uid), true);
     }
 
-    public override void Shutdown()
-    {
-        _prototypeManager.PrototypesReloaded -= HandlePrototypesReloaded;
-
-        base.Shutdown();
-    }
-
     private void HandlePrototypesReloaded(PrototypesReloadedEventArgs obj)
     {
-        LoadPrototypes();
+        if (obj.WasModified<AlertPrototype>())
+            LoadPrototypes();
     }
 
     protected virtual void LoadPrototypes()
     {
-        _typeToAlert.Clear();
+        var dict = new Dictionary<AlertType, AlertPrototype>();
         foreach (var alert in _prototypeManager.EnumeratePrototypes<AlertPrototype>())
         {
-            if (!_typeToAlert.TryAdd(alert.AlertType, alert))
+            if (!dict.TryAdd(alert.AlertType, alert))
             {
                 Log.Error("Found alert with duplicate alertType {0} - all alerts must have" +
                           " a unique alerttype, this one will be skipped", alert.AlertType);
             }
         }
+
+        _typeToAlert = dict.ToFrozenDictionary();
     }
 
     /// <summary>