Click Drag Functionality + Refactor Interaction Interfaces (#1125)

Co-authored-by: Víctor Aguilera Puerto <6766154+Zumorica@users.noreply.github.com>
Co-authored-by: ComicIronic <comicironic@gmail.com>
Co-authored-by: Pieter-Jan Briers <pieterjan.briers+git@gmail.com>

Content.Server/Interfaces/GameObjects/Components/Interaction/IDropped.cs

@@ -0,0 +1,53 @@
+using System;
+using JetBrains.Annotations;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Interfaces.GameObjects;
+
+namespace Content.Server.Interfaces.GameObjects.Components.Interaction
+{
+    /// <summary>
+    ///     This interface gives components behavior when they're dropped by a mob.
+    /// </summary>
+    public interface IDropped
+    {
+        void Dropped(DroppedEventArgs eventArgs);
+    }
+
+    public class DroppedEventArgs : EventArgs
+    {
+        public DroppedEventArgs(IEntity user)
+        {
+            User = user;
+        }
+
+        public IEntity User { get; }
+    }
+
+    /// <summary>
+    ///     Raised when an entity is dropped
+    /// </summary>
+    [PublicAPI]
+    public class DroppedMessage : EntitySystemMessage
+    {
+        /// <summary>
+        ///     If this message has already been "handled" by a previous system.
+        /// </summary>
+        public bool Handled { get; set; }
+
+        /// <summary>
+        ///     Entity that dropped the item.
+        /// </summary>
+        public IEntity User { get; }
+
+        /// <summary>
+        ///     Item that was dropped.
+        /// </summary>
+        public IEntity Dropped { get; }
+
+        public DroppedMessage(IEntity user, IEntity dropped)
+        {
+            User = user;
+            Dropped = dropped;
+        }
+    }
+}