Add code coverage for DataGridViewColumnTypePicker (#13055)

Related #10773

## Proposed changes
Add unit test file: DataGridViewColumnTypePicker.cs for public methods
of the DataGridViewColumnTypePicker.cs

Author: Zheng-Li01

src/System.Windows.Forms.Design/tests/UnitTests/System/Windows/Forms/Design/DataGridViewColumnTypePickerTests.cs

@@ -0,0 +1,83 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.ComponentModel.Design;
+using System.Drawing;
+using Moq;
+
+namespace System.Windows.Forms.Design.Tests;
+
+public class DataGridViewColumnTypePickerTests : IDisposable
+{
+    private readonly DataGridViewColumnTypePicker _picker;
+
+    public DataGridViewColumnTypePickerTests()
+    {
+        _picker = new();
+    }
+
+    public void Dispose() => _picker.Dispose();
+
+    [Fact]
+    public void Constructor_ShouldInitializeListBoxCorrectly()
+    {
+        _picker.Controls.Count.Should().Be(1);
+        _picker.Controls[0].Should().BeOfType<ListBox>().Which.Should().Match<ListBox>(listBox =>
+            listBox.Dock == DockStyle.Fill
+            && listBox.Sorted
+            && listBox.HorizontalScrollbar);
+    }
+
+    [Fact]
+    public void Constructor_ShouldSetBackColorAndActiveControl()
+    {
+        _picker.BackColor.Should().Be(SystemColors.Control);
+        _picker.ActiveControl.Should().Be(_picker.Controls[0]);
+    }
+
+    [Fact]
+    public void SelectedType_ShouldReturnNull_WhenNotSet() =>
+        _picker.SelectedType.Should().BeNull();
+
+    [Fact]
+    public void Start_ShouldPopulateListBoxItems()
+    {
+        Mock<IWindowsFormsEditorService> editorServiceMock = new();
+        Mock<ITypeDiscoveryService> discoveryServiceMock = new();
+        List<Type> types = [typeof(DataGridViewTextBoxColumn), typeof(DataGridViewButtonColumn)];
+        discoveryServiceMock.Setup(ds => ds.GetTypes(It.IsAny<Type>(), It.IsAny<bool>())).Returns(types);
+
+        _picker.Start(editorServiceMock.Object, discoveryServiceMock.Object, typeof(DataGridViewTextBoxColumn));
+
+        var listBox = _picker.TestAccessor().Dynamic._typesListBox;
+        object count = listBox.Items.Count;
+        count.Should().Be(2);
+    }
+
+    [Fact]
+    public void SetBoundsCore_ShouldSetMinimumWidthAndHeight()
+    {
+        var accessor = _picker.TestAccessor().Dynamic;
+        accessor.SetBoundsCore(0, 0, 50, 50, BoundsSpecified.All);
+
+        _picker.Width.Should().BeGreaterOrEqualTo(100);
+        _picker.Height.Should().BeGreaterOrEqualTo(90);
+    }
+
+    [Fact]
+    public void typesListBox_SelectedIndexChanged_ShouldSetSelectedType()
+    {
+        Mock<IWindowsFormsEditorService> editorServiceMock = new();
+        Mock<ITypeDiscoveryService> discoveryServiceMock = new();
+        List<Type> types = [typeof(DataGridViewTextBoxColumn), typeof(DataGridViewButtonColumn)];
+        discoveryServiceMock.Setup(ds => ds.GetTypes(It.IsAny<Type>(), It.IsAny<bool>())).Returns(types);
+
+        _picker.Start(editorServiceMock.Object, discoveryServiceMock.Object, typeof(DataGridViewTextBoxColumn));
+        var listBox = _picker.TestAccessor().Dynamic._typesListBox;
+        listBox.SelectedIndex = 1;
+
+        _picker.TestAccessor().Dynamic.typesListBox_SelectedIndexChanged(listBox, EventArgs.Empty);
+
+        _picker.SelectedType.Should().Be(typeof(DataGridViewTextBoxColumn));
+    }
+}