Fix stage line alignment in mania not matching stable

Author: frenzibyte

Diff for: osu.Game.Rulesets.Mania/Skinning/Legacy/LegacyStageBackground.cs

@@ -54,7 +54,8 @@ private void load(ISkinSource skin, StageDefinition stageDefinition)
                 },
                 columnBackgrounds = new ColumnFlow<Drawable>(stageDefinition)
                 {
-                    RelativeSizeAxes = Axes.Y
+                    RelativeSizeAxes = Axes.Y,
+                    Masking = false,
                 },
                 new HitTargetInsetContainer
                 {
@@ -126,8 +127,8 @@ private void load(ISkinSource skin)
                             },
                             new Container
                             {
+                                X = isLastColumn ? -0.16f : 0,
                                 Anchor = Anchor.TopRight,
-                                Origin = Anchor.TopRight,
                                 RelativeSizeAxes = Axes.Y,
                                 Width = rightLineWidth,
                                 Scale = new Vector2(0.740f, 1),

Diff for: osu.Game.Rulesets.Mania/UI/ColumnFlow.cs

@@ -28,6 +28,12 @@ public partial class ColumnFlow<TContent> : CompositeDrawable
         private readonly FillFlowContainer<Container<TContent>> columns;
         private readonly StageDefinition stageDefinition;
 
+        public new bool Masking
+        {
+            get => base.Masking;
+            set => base.Masking = value;
+        }
+
         public ColumnFlow(StageDefinition stageDefinition)
         {
             this.stageDefinition = stageDefinition;