Rewrite PlaceholderManager4KB to use intrusive RBTree, and to coalesce free placeholders

Also make the other placeholder manager use intrusive RBTree, allows the IntervalTree that was added just for this to be deleted

Ryujinx.Memory/WindowsShared/MappingTree.cs

@@ -0,0 +1,69 @@
+using Ryujinx.Common.Collections;
+using System;
+
+namespace Ryujinx.Memory.WindowsShared
+{
+    /// <summary>
+    /// A intrusive Red-Black Tree that also supports getting nodes overlapping a given range.
+    /// </summary>
+    /// <typeparam name="T">Type of the value stored on the node</typeparam>
+    class MappingTree<T> : IntrusiveRedBlackTree<RangeNode<T>>
+    {
+        public int GetNodes(ulong start, ulong end, ref RangeNode<T>[] overlaps, int overlapCount = 0)
+        {
+            RangeNode<T> node = GetNode(new RangeNode<T>(start, start + 1UL, default));
+
+            for (; node != null; node = node.Successor)
+            {
+                if (overlaps.Length <= overlapCount)
+                {
+                    Array.Resize(ref overlaps, overlapCount + 1);
+                }
+
+                overlaps[overlapCount++] = node;
+
+                if (node.End >= end)
+                {
+                    break;
+                }
+            }
+
+            return overlapCount;
+        }
+    }
+
+    class RangeNode<T> : IntrusiveRedBlackTreeNode<RangeNode<T>>, IComparable<RangeNode<T>>
+    {
+        public ulong Start { get; }
+        public ulong End { get; private set; }
+        public T Value { get; }
+
+        public RangeNode(ulong start, ulong end, T value)
+        {
+            Start = start;
+            End = end;
+            Value = value;
+        }
+
+        public void Extend(ulong sizeDelta)
+        {
+            End += sizeDelta;
+        }
+
+        public int CompareTo(RangeNode<T> other)
+        {
+            if (Start < other.Start)
+            {
+                return -1;
+            }
+            else if (Start <= other.End - 1UL)
+            {
+                return 0;
+            }
+            else
+            {
+                return 1;
+            }
+        }
+    }
+}