Turn SandboxManager into a system (#6867)

Content.Shared/Sandbox/SharedSandboxSystem.cs

@@ -0,0 +1,28 @@
+using Robust.Shared.Prototypes;
+using Robust.Shared.Serialization;
+
+namespace Content.Shared.Sandbox
+{
+    public abstract class SharedSandboxSystem : EntitySystem
+    {
+        [Dependency] protected readonly IPrototypeManager PrototypeManager = default!;
+
+        [Serializable, NetSerializable]
+        protected sealed class MsgSandboxStatus : EntityEventArgs
+        {
+            public bool SandboxAllowed { get; set; }
+        }
+
+        [Serializable, NetSerializable]
+        protected sealed class MsgSandboxRespawn : EntityEventArgs {}
+
+        [Serializable, NetSerializable]
+        protected sealed class MsgSandboxGiveAccess : EntityEventArgs {}
+
+        [Serializable, NetSerializable]
+        protected sealed class MsgSandboxGiveAghost : EntityEventArgs {}
+
+        [Serializable, NetSerializable]
+        protected sealed class MsgSandboxSuicide : EntityEventArgs {}
+    }
+}