Add back right-click-for-new-combo and right-click-delete when in com…

…pose mode

Requested too many times to count.

I'm not sure what to do about the code quality of this. It's a bit weird
that there's no way to check the current composition tool from a higher
level.

Also it was discussed IRL that there should be some kind of hinting that
existing notes will be deleted when they are hovered, but I'm not sure
how well this will work in normal mapping flows, since it will display
even in cases that users aren't intending to delete an object. Still
willing to explore this direction though (it's just non-trivial to
implement so I haven't yet).

osu.Game.Rulesets.Osu/Edit/OsuHitObjectComposer.cs

@@ -30,6 +30,7 @@
 using osu.Game.Screens.Edit.Components.TernaryButtons;
 using osu.Game.Screens.Edit.Compose.Components;
 using osuTK;
+using osuTK.Input;
 
 namespace osu.Game.Rulesets.Osu.Edit
 {
@@ -351,6 +352,19 @@ private void updateDistanceSnapGrid()
             }
         }
 
+        protected override bool OnMouseDown(MouseDownEvent e)
+        {
+            if (e.Button == MouseButton.Right)
+            {
+                var osuSelectionHandler = (OsuSelectionHandler)BlueprintContainer.SelectionHandler;
+
+                osuSelectionHandler.SelectionNewComboState.Value =
+                    osuSelectionHandler.SelectionNewComboState.Value == TernaryState.False ? TernaryState.True : TernaryState.False;
+            }
+
+            return base.OnMouseDown(e);
+        }
+
         protected override bool OnKeyDown(KeyDownEvent e)
         {
             if (e.Repeat)

osu.Game/Screens/Edit/Compose/Components/ComposeBlueprintContainer.cs

@@ -387,6 +387,9 @@ public CompositionTool CurrentTool
 
                 currentTool = value;
 
+                // Maybe this should go in EditorState or somewhere else? Feels a bit haphazard.
+                SelectionHandler.IsInSelectionMode = currentTool is SelectTool;
+
                 // As per stable editor, when changing tools, we should forcefully commit any pending placement.
                 CommitIfPlacementActive();
             }

osu.Game/Screens/Edit/Compose/Components/SelectionHandler.cs

@@ -30,6 +30,8 @@ namespace osu.Game.Screens.Edit.Compose.Components
     /// </summary>
     public abstract partial class SelectionHandler<T> : CompositeDrawable, IKeyBindingHandler<PlatformAction>, IKeyBindingHandler<GlobalAction>, IHasContextMenu
     {
+        public bool IsInSelectionMode { get; set; }
+
         /// <summary>
         /// How much padding around the selection area is added.
         /// </summary>
@@ -271,7 +273,7 @@ internal virtual void HandleDeselected(SelectionBlueprint<T> blueprint)
         /// <returns>Whether a selection was performed.</returns>
         internal virtual bool MouseDownSelectionRequested(SelectionBlueprint<T> blueprint, MouseButtonEvent e)
         {
-            if (e.Button == MouseButton.Middle || (e.ShiftPressed && e.Button == MouseButton.Right))
+            if (e.Button == MouseButton.Middle || (!IsInSelectionMode || (e.ShiftPressed && e.Button == MouseButton.Right)))
             {
                 handleQuickDeletion(blueprint);
                 return true;