Add utility AI (#806)

Co-authored-by: Pieter-Jan Briers <pieterjan.briers@gmail.com>
Co-authored-by: Metal Gear Sloth <metalgearsloth@gmail.com>
Co-authored-by: Pieter-Jan Briers <pieterjan.briers+git@gmail.com>

Content.Server/AI/Operators/AiOperator.cs

@@ -0,0 +1,55 @@
+
+using System;
+
+namespace Content.Server.AI.Operators
+{
+    public abstract class AiOperator
+    {
+        private bool _hasStartup = false;
+        private bool _hasShutdown = false;
+
+        /// <summary>
+        /// Called once when the AiLogicProcessor starts this action
+        /// </summary>
+        public virtual bool TryStartup()
+        {
+            // If we've already startup then no point continuing
+            // This signals to the override that it's already startup
+            // Should probably throw but it made some code elsewhere marginally easier
+            if (_hasStartup)
+            {
+                return false;
+            }
+            
+            _hasStartup = true;
+            return true;
+        }
+
+        /// <summary>
+        /// Called once when the AiLogicProcessor is done with this action if the outcome is successful or fails.
+        /// </summary>
+        public virtual void Shutdown(Outcome outcome)
+        {
+            if (_hasShutdown)
+            {
+                throw new InvalidOperationException("AiOperator has already shutdown");
+            }
+
+            _hasShutdown = true;
+        }
+
+        /// <summary>
+        /// Called every tick for the AI
+        /// </summary>
+        /// <param name="frameTime"></param>
+        /// <returns></returns>
+        public abstract Outcome Execute(float frameTime);
+    }
+
+    public enum Outcome
+    {
+        Success,
+        Continuing,
+        Failed,
+    }
+}