Add `WatchList.InsertRange` and use when duplicating rows in RAM Watch

src/BizHawk.Client.Common/tools/Watch/WatchList/WatchList.cs

@@ -143,6 +143,21 @@ namespace BizHawk.Client.Common
 			Changes = true;
 		}
 
+		/// <param name="index">
+		/// <c>0</c> to prepend, <see cref="Count"/> to append, anything in-between to insert there
+		/// (the first elem of <paramref name="collection"/> will end up at <paramref name="index"/>)
+		/// </param>
+		public void InsertRange(int index, IEnumerable<Watch> collection)
+		{
+#if NET6_0
+			if (collection.TryGetNonEnumeratedCount(out var n) && n is 0) return;
+#else
+			if (collection is ICollection<Watch> hasCount && hasCount.Count is 0) return;
+#endif
+			_watchList.InsertRange(index, collection);
+			Changes = true;
+		}
+
 		/// <summary>
 		/// Removes item at the specified index
 		/// </summary>

src/BizHawk.Client.EmuHawk/tools/Watch/RamWatch.cs

@@ -411,7 +411,7 @@ namespace BizHawk.Client.EmuHawk
 				{
 					if (duplicate)
 					{
-						_watches.AddRange(we.Watches);
+						_watches.InsertRange(WatchListView.SelectionEndIndex!.Value + 1, we.Watches); //TODO should be able to reduce the number of enumerations of selected rows if necessary --yoshi
 						WatchListView.RowCount = _watches.Count;
 						UpdateWatchCount();
 					}