Move custom visuals into basic implementation

osu.Framework/Graphics/Containers/BasicScrollContainer.cs

···
 
         protected override ScrollbarContainer CreateScrollbar(Direction direction) => new BasicScrollbar(direction);
 
-        protected class BasicScrollbar : ScrollbarContainer
+        protected internal class BasicScrollbar : ScrollbarContainer
         {
             private const float dim_size = 8;
 

osu.Framework/Graphics/Containers/RearrangeableListContainer.cs

···
         /// <summary>
         /// Creates the <see cref="ListScrollContainer"/> for the list of items.
         /// </summary>
-        protected virtual ListScrollContainer CreateListScrollContainer(ListFillFlowContainer flowContainer) => new ListScrollContainer(flowContainer);
+        protected abstract ListScrollContainer CreateListScrollContainer(ListFillFlowContainer flowContainer);
 
         /// <summary>
         /// Creates the <see cref="Drawable"/> representation of an item.
···
 
         #region ListScrollContainer
 
-        protected class ListScrollContainer : BasicScrollContainer<ListFillFlowContainer>
+        protected abstract class ListScrollContainer : ScrollContainer<ListFillFlowContainer>
         {
             private const float scroll_trigger_distance = 10;
             private const double max_power = 50;
···
             private bool autoScrolling;
             private double scrollSpeed;
 
-            public ListScrollContainer(ListFillFlowContainer flowContainer)
+            protected ListScrollContainer(ListFillFlowContainer flowContainer)
             {
                 RelativeSizeAxes = Axes.Both;
-                ScrollbarOverlapsContent = false;
-                Padding = new MarginPadding(5);
 
                 Child = flowContainer.With(d =>
                 {

osu.Framework/Graphics/UserInterface/BasicRearrangeableListContainer.cs

···
 
         public bool ShowRemoveButton = true;
 
+        protected override ListScrollContainer CreateListScrollContainer(ListFillFlowContainer flowContainer) => new BasicListScrollContainer(flowContainer);
+
         protected override DrawableRearrangeableListItem CreateDrawable(BasicRearrangeableItem item) => new BasicDrawableRearrangeableListItem(item)
         {
             UseDragHandle = UseDragHandle,
             ShowRemoveButton = ShowRemoveButton,
         };
+
+        protected class BasicListScrollContainer : ListScrollContainer
+        {
+            public BasicListScrollContainer(ListFillFlowContainer flowContainer)
+                : base(flowContainer)
+            {
+                ScrollbarOverlapsContent = false;
+                Padding = new MarginPadding(5);
+            }
+
+            // Todo: This isn't good.
+            protected override ScrollbarContainer CreateScrollbar(Direction direction) => new BasicScrollContainer<ListFillFlowContainer>.BasicScrollbar(direction);
+        }
 
         public class BasicDrawableRearrangeableListItem : DrawableRearrangeableListItem
         {