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/IDragDropOn.cs

@@ -0,0 +1,24 @@
+using System;
+using Content.Server.Interfaces.GameObjects.Components.Interaction;
+using Robust.Shared.Interfaces.GameObjects;
+using Robust.Shared.Map;
+
+namespace Content.Server.Interfaces.GameObjects.Components.Interaction
+{
+    /// <summary>
+    /// This interface allows the component's entity to be dragged and dropped onto by another entity and gives it
+    /// behavior when that occurs.
+    /// </summary>
+    public interface IDragDropOn
+    {
+        /// <summary>
+        /// Invoked server-side when another entity is being dragged and dropped onto this one
+        ///
+        /// There is no other server-side drag and drop check other than a range check, so make sure to validate
+        /// if this object can be dropped on the dropped object!
+        /// </summary>
+        /// <returns>true iff an interaction occurred and no further interaction should
+        /// be processed for this drop.</returns>
+        bool DragDropOn(DragDropEventArgs eventArgs);
+    }
+}