Ensure that classes in the System.Windows.Forms namespace have adequate unit test coverage

Please start with classes with coverage **below 20%** (marked in red in the [codecov.io](https://app.codecov.io/gh/dotnet/winforms/tree/main/src%2FSystem.Windows.Forms%2FSystem%2FWindows%2FForms%2FControls), and prioritize `public` and `protected virtual` methods.

**Note:** Some private classes cannot be tested

- **Controls/Buttons**:

- [x] ButtonRenderer.cs - 19.88% #13745
- [x] ButtonFlatAdapter.cs – 14.91% #13743
- [x] ButtonPopupAdapter.cs – 16.39% #13731
- [x] CheckBoxBaseAdapter.cs – 16.97% #13752
- [x] CheckBoxFlatAdapter.cs – 4.48% #13751
- [x] CheckBoxPopupAdapter.cs – 2.59% #13755
- [x] RadioButtonBaseAdapter.cs – 9.27% #13726
- [ ] RadioButtonFlatAdapter.cs – 1.64%
- [ ] RadioButtonPopupAdapter.cs – 1.52%

- **DataGridView**:

- [x] ~~DataGridViewButtonCell.DataGridViewButtonCellRenderer.cs – 0.00%~~ _(private class)_
- [x] DataGridViewButtonCell.cs – 6.16% #13667
- [x] ~~DataGridViewCheckBoxCell.DataGridViewCheckBoxCellRenderer.cs – 0.00%~~ _(private class)_
- [x] ~~DataGridViewComboBoxCell.DataGridViewComboBoxCellRenderer.cs – 0.00%~~ _(private class)_
- [x] DataGridViewComboBoxCell.cs – 15.49% #13654
- [x] DataGridViewComboBoxColumn.cs – 7.12% #13617
- [x] DataGridViewImageCell.cs – 8.13% #13616
- [x] DataGridViewImageColumn.cs – 11.18% #13547
- [x] DataGridViewLinkCell.cs – 11.97% #13524

- **DateTimePicker**:

- [x] ~~DateTimePicker.EnumChildren.cs - 0%~~ _(private class)_

- **ImageList**:

- [x] ImageListConverter.cs #13511

- **ListView**:

- [x] ListView.CheckedListViewItemCollection.cs – 18.34% #13685
- [x] ListView.IconComparer.cs – 0.00% #13485
- [ ] ListView.ListViewItemCollection.IInnerList.cs – 0.00%
- [x] ListViewItemStateImageIndexConverter.cs – 15.22% #13716

- **PropertyGrid/PropertyGridInternal**:

- [x] ArrayElementGridEntry.cs – 0.00% #13537
- [x] GridEntryRecreateChildrenEventArgs.cs – 0.00% #13497
- [x] GridToolTip.cs – 19.17% #13533
- [x] ~~MergePropertyDescriptor.MultiMergeCollection.cs – 0.00%~~ _(private class)_
- [x] MultiPropertyDescriptorGridEntry.cs – 6.77% #13713
- [x] ~~PropertyDescriptorGridEntry.ExceptionConverter.cs – 0.00%~~ _(private class)_
- [x] ~~PropertyDescriptorGridEntry.ExceptionEditor.cs – 0.00%~~ _(private class)_
- [x] PropertyGridCommands.cs – 0.00% #13495

- **Splitter**:
- [x] ~~Splitter.SplitterMessageFilter.cs - 0%~~ _(private class)_

- **TabControl**:

- [x] TabRenderer.cs - 0% #13482

- **ToolStrips**:

- [ ] ToolStrip.RestoreFocusMessageFilter.cs – 14.81%
- [x] ToolStripContainer.ToolStripContainerTypedControlCollection.cs – 13.33% #13527
- [x] ToolStripManager.ModalMenuFilter.HostedWindowsFormsMessageHook.cs – 0.00% #13762
- [x] ~~ToolStripPanel.FeedbackRectangle.FeedbackDropDown.cs – 0.00%~~ _(private class)_
- [x] ~~ToolStripPanel.FeedbackRectangle.cs – 0.00%~~ _(private class)_
- [x] ToolStripProfessionalLowResolutionRenderer.cs – 0.00% #13691

- **UpDown**:

- [x] DomainUpDown.DomainItemAccessibleObject.cs – 0.00% #13484
- [x] ~~DomainUpDown.DomainUpDownAccessibleObject.cs~~ – This class was obsoleted
- [x] UpDownBase.UpDownBaseAccessibleObject.cs – 16.67% #13498

- **WebBrowser**:

- [x] HtmlElementErrorEventArgs.cs – 0.00% #13512
- [ ] HtmlHistory.cs – 0.00%
- [x] ~~HtmlWindow.HTMLWindowEvents2.cs – 0.00%~~ _(private class)_
- [ ] WebBrowserContainer.cs – 11.70% #14006
- [x] WebBrowserUriTypeConverter.cs – 0.00% #13523