Add code coverage for ToolStripPanelControlCollection_XYComparer (#12711

)

related #10453

Proposed changes
Add unit tests for ToolStripPanelControlCollectionXYComparer.cs to test its methods

src/System.Windows.Forms/tests/UnitTests/System/Windows/Forms/ToolStripPanel.ToolStripPanelControlCollection.XYComparerTests.cs

@@ -0,0 +1,46 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#nullable enable
+
+using System.Drawing;
+
+namespace System.Windows.Forms.Tests;
+
+public class ToolStripPanel_ToolStripPanelControlCollection_XYComparerTests
+{
+    private readonly ToolStripPanel.ToolStripPanelControlCollection.XYComparer _comparer = new();
+    private readonly Control _control1 = new() { Bounds = new Rectangle(10, 20, 100, 100) };
+    private readonly Control _control2 = new() { Bounds = new Rectangle(10, 10, 100, 100) };
+
+    public void Dispose()
+    {
+        _control1.Dispose();
+        _control2.Dispose();
+    }
+
+    [WinFormsFact]
+    public void Compare_FirstControlNull_ReturnsNegativeOne() =>
+        _comparer.Compare(null, _control1).Should().Be(-1);
+
+    [WinFormsFact]
+    public void Compare_SecondControlNull_ReturnsOne() =>
+        _comparer.Compare(_control1, null).Should().Be(1);
+
+    [WinFormsFact]
+    public void Compare_BothControlsNull_ReturnsZero() =>
+        _comparer.Compare(null, null).Should().Be(0);
+
+    [WinFormsTheory]
+    [InlineData(10, 10, 20, 10, -1)]
+    [InlineData(10, 10, 10, 20, -1)]
+    [InlineData(10, 20, 10, 10, 1)]
+    [InlineData(20, 10, 10, 10, 1)]
+    public void Compare_VariousBounds_ReturnsExpected(int x1, int y1, int x2, int y2, int expected)
+    {
+        _control1.Bounds = new Rectangle(x1, y1, 100, 100);
+        _control2.Bounds = new Rectangle(x2, y2, 100, 100);
+
+        _comparer.Compare(_control1, _control2).Should().Be(expected);
+    }
+}