Actions System + UI (#2710)

Co-authored-by: Vera Aguilera Puerto <6766154+Zumorica@users.noreply.github.com>

Content.Shared/Actions/ITargetEntityAction.cs

@@ -0,0 +1,33 @@
+using System;
+using Robust.Shared.Interfaces.GameObjects;
+using Robust.Shared.Interfaces.Serialization;
+using Robust.Shared.Map;
+
+namespace Content.Shared.Actions
+{
+    /// <summary>
+    /// Action which is used on a targeted entity.
+    /// </summary>
+    public interface ITargetEntityAction : IActionBehavior
+    {
+        /// <summary>
+        /// Invoked when the target entity action should be performed.
+        /// Implementation should perform the server side logic of the action.
+        /// </summary>
+        void DoTargetEntityAction(TargetEntityActionEventArgs args);
+    }
+
+    public class TargetEntityActionEventArgs : ActionEventArgs
+    {
+        /// <summary>
+        /// Entity being targeted
+        /// </summary>
+        public readonly IEntity Target;
+
+        public TargetEntityActionEventArgs(IEntity performer, ActionType actionType, IEntity target) :
+            base(performer, actionType)
+        {
+            Target = target;
+        }
+    }
+}