[sortablejs] adds some missing event properties (#41160)

* [sortablejs] creates clear description for fake class

* [sortablejs] add some swap and multidrag event options

types/sortablejs/index.d.ts

@@ -96,7 +96,7 @@ declare namespace Sortable {
             SwapOptions {}
 
     /**
-     * A class that all plugins inherit from for the sake of types
+     * A class that all plugins inherit from for the sake of type inference.
      */
     export class Plugin extends SortablePlugin {}
     export class MultiDrag extends MultiDragPlugin {}
@@ -139,6 +139,24 @@ declare namespace Sortable {
          * Pull mode if dragging into another sortable
          */
         pullMode: 'clone' | boolean | undefined;
+        /**
+         * When MultiDrag is used to sort, this holds a HTMLElement and oldIndex for each item selected.
+         *
+         * `oldIndicies[number]` is directly related to `newIndicies[number]`
+         *
+         * If MultiDrag is not used to sort, this array will be empty.
+         */
+        oldIndicies: { multiDragElement: HTMLElement; index: number }[];
+        /**
+         * When MultiDrag is used to sort, this holds a HTMLElement and newIndex for each item.
+         *
+         * `oldIndicies[number]` is directly related to `newIndicies[number]`
+         *
+         * If MultiDrag is not used to sort, this array will be empty.
+         */
+        newIndicies: { multiDragElement: HTMLElement; index: number }[];
+        /** When Swap is used to sort, this will contain the dragging item that was dropped on.*/
+        swapItem: HTMLElement | null;
     }
 
     export interface MoveEvent extends Event {