Use HashSet to track GraphicsDevice resources (MonoGame#9027)

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Improves performance of `GraphicsDevice.RemoveResourceReference` (and by
extension `GraphicsResource.Dispose`) when there are a lot of resources.

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### Description of Change

`List<T>.Remove(T item)` needs to iterate every item of the list to find
the one to remove, then shift items when removing from the middle.
HashSet<T> has much faster deletion, at the cost of a slightly slower
insert.

My specific example had over 30000 resources, and triggered large
stutters when clearing a cache with around 4000 recently allocated
items. It was iterating approximately 120000000 resources removing these
entries, since they would be at the end of the list.

My test case was a little extreme since I was scrolling a map with a
huge number of unique models that stream in+out, but it's an easy
improvement to make.

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Author: riperiperi

MonoGame.Framework/Graphics/GraphicsDevice.cs

@@ -7,7 +7,8 @@
 using System.Diagnostics;
 using System.Globalization;
 using MonoGame.Framework.Utilities;
-using System.Runtime.InteropServices;
+using System.Runtime.InteropServices;
+using System.Linq;
 
 
 namespace Microsoft.Xna.Framework.Graphics
@@ -154,7 +155,7 @@ private bool PixelShaderDirty
         // Use WeakReference for the global resources list as we do not know when a resource
         // may be disposed and collected. We do not want to prevent a resource from being
         // collected by holding a strong reference to it in this list.
-        private readonly List<WeakReference> _resources = new List<WeakReference>();
+        private readonly HashSet<WeakReference> _resources = new HashSet<WeakReference>();
 
         // TODO Graphics Device events need implementing
         /// <summary>
@@ -804,7 +805,7 @@ internal void OnDeviceResetting()
                 }
 
                 // Remove references to resources that have been garbage collected.
-                _resources.RemoveAll(wr => !wr.IsAlive);
+                _resources.RemoveWhere(wr => !wr.IsAlive);
             }
         }
 

Tests/Framework/Graphics/GraphicsDeviceTest.cs

@@ -852,5 +852,32 @@ public void GetBackBufferData(Rectangle? rectangle)
 
             CheckFrames();
         }
+
+        [Test]
+        [RunOnUI]
+        public void DisposeReferencedResources()
+        {
+            var rt = new RenderTarget2D(gdm.GraphicsDevice, 5, 5);
+            var vb = new DynamicVertexBuffer(gd, VertexPositionColor.VertexDeclaration, 1, BufferUsage.None);
+
+            var middleIb = new DynamicIndexBuffer(gd, IndexElementSize.SixteenBits, 1, BufferUsage.None);
+
+            var ib = new DynamicIndexBuffer(gd, IndexElementSize.SixteenBits, 1, BufferUsage.None);
+            var rtc = new RenderTargetCube(gd, 1, false, SurfaceFormat.Color, DepthFormat.Depth16);
+
+            middleIb.Dispose();
+            Assert.IsTrue(middleIb.IsDisposed);
+
+            // Remaining referenced resources should be disposed.
+            gd.Dispose();
+
+            Assert.IsTrue(rt.IsDisposed);
+
+            Assert.IsTrue(vb.IsDisposed);
+
+            Assert.IsTrue(ib.IsDisposed);
+
+            Assert.IsTrue(rtc.IsDisposed);
+        }
     }
 }