re-add library scan from library manager

Emby.Server.Implementations/Library/LibraryManager.cs

@@ -2453,6 +2453,12 @@ namespace Emby.Server.Implementations.Library
             return RootFolder;
         }
 
+        /// <inheritdoc />
+        public void QueueLibraryScan()
+        {
+            _taskManager.QueueScheduledTask<RefreshMediaLibraryTask>();
+        }
+
         /// <inheritdoc />
         public int? GetSeasonNumberFromPath(string path)
             => SeasonPathParser.Parse(path, true, true).SeasonNumber;

MediaBrowser.Controller/Library/ILibraryManager.cs

@@ -570,5 +570,13 @@ namespace MediaBrowser.Controller.Library
         Task RunMetadataSavers(BaseItem item, ItemUpdateType updateReason);
 
         BaseItem GetParentItem(Guid? parentId, Guid? userId);
+
+        /// <summary>
+        /// Queue a library scan.
+        /// </summary>
+        /// <remarks>
+        /// This exists so plugins can trigger a library scan.
+        /// </remarks>
+        void QueueLibraryScan();
     }
 }