do_after (#1616)

* do_after

Ports (most of) do_after from SS13.
Callers are expected to await the DoAfter task from the DoAfterSystem.
I had a dummy component for in-game testing which I removed for the PR so nothing in game uses do_after at the moment.
Currently only the movement cancellation is predicted client-side.

* Minor do_after doc cleanup

* do_the_shuffle

Fix nullable build errors.

* The last nullable

* Implement NeedHand

Thanks zum.

* nullable dereference

* Adjust the system query

Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>

Content.Server/GameObjects/EntitySystems/DoAfter/DoAfterEventArgs.cs

@@ -0,0 +1,84 @@
+#nullable enable
+using System;
+using System.Threading;
+using Robust.Shared.Interfaces.GameObjects;
+
+namespace Content.Server.GameObjects.EntitySystems
+{
+    public sealed class DoAfterEventArgs
+    {
+        /// <summary>
+        ///     The entity invoking do_after
+        /// </summary>
+        public IEntity User { get; }
+        
+        /// <summary>
+        ///     How long does the do_after require to complete
+        /// </summary>
+        public float Delay { get; }
+
+        /// <summary>
+        ///     Applicable target (if relevant)
+        /// </summary>
+        public IEntity? Target { get; }
+        
+        /// <summary>
+        ///     Manually cancel the do_after so it no longer runs
+        /// </summary>
+        public CancellationToken CancelToken { get; }
+        
+        // Break the chains
+        /// <summary>
+        ///     Whether we need to keep our active hand as is (i.e. can't change hand or change item).
+        ///     This also covers requiring the hand to be free (if applicable).
+        /// </summary>
+        public bool NeedHand { get; }
+        
+        /// <summary>
+        ///     If do_after stops when the user moves
+        /// </summary>
+        public bool BreakOnUserMove { get; }
+        
+        /// <summary>
+        ///     If do_after stops when the target moves (if there is a target)
+        /// </summary>
+        public bool BreakOnTargetMove { get; }
+        public bool BreakOnDamage { get; }
+        public bool BreakOnStun { get; }
+        
+        /// <summary>
+        ///     Additional conditions that need to be met. Return false to cancel.
+        /// </summary>
+        public Func<bool>? ExtraCheck { get; }
+        
+        public DoAfterEventArgs(
+            IEntity user, 
+            float delay,
+            CancellationToken cancelToken,
+            IEntity? target = null,
+            bool needHand = true,
+            bool breakOnUserMove = true,
+            bool breakOnTargetMove = true,
+            bool breakOnDamage = true,
+            bool breakOnStun = true,
+            Func<bool>? extraCheck = null
+        )
+        {
+            User = user;
+            Delay = delay;
+            CancelToken = cancelToken;
+            Target = target;
+            NeedHand = needHand;
+            BreakOnUserMove = breakOnUserMove;
+            BreakOnTargetMove = breakOnTargetMove;
+            BreakOnDamage = breakOnDamage;
+            BreakOnStun = breakOnStun;
+            ExtraCheck = extraCheck;
+            
+            if (Target == null)
+            {
+                BreakOnTargetMove = false;
+            }
+        }
+    }
+}