`DependencyProperty.GetMetadata` doesn't handle custom types correctly

### Describe the bug

Passing a custom type to `DependencyProperty.GetMetadata` doesn't get recognized correctly and the returned metadata can have wrong default value.

### Steps to reproduce the bug

```csharp
public sealed partial class MainWindow : Window
{
public MainWindow()
{
this.InitializeComponent();
When_IsTabStop();
}

private partial class CustomFE : FrameworkElement { }
private partial class CustomControl : Control { }
private partial class CustomUserControl : UserControl { }

private static class Assert
{
public static void IsFalse(bool b)
{
if (b)
{
throw new Exception();
}
}

public static void IsTrue(bool b)
{
if (!b)
{
throw new Exception();
}
}
}

public void When_IsTabStop()
{
var customControl = new CustomControl();
Assert.IsTrue(customControl.IsTabStop);

var userControl = new UserControl();
Assert.IsFalse(userControl.IsTabStop);

var customUserControl = new CustomUserControl();
Assert.IsFalse(customUserControl.IsTabStop);

Assert.IsFalse((bool)Control.IsTabStopProperty.GetMetadata(typeof(UIElement)).DefaultValue);
Assert.IsFalse((bool)Control.IsTabStopProperty.GetMetadata(typeof(FrameworkElement)).DefaultValue);
Assert.IsFalse((bool)Control.IsTabStopProperty.GetMetadata(typeof(CustomFE)).DefaultValue);
Assert.IsTrue((bool)Control.IsTabStopProperty.GetMetadata(typeof(Control)).DefaultValue);
Assert.IsFalse((bool)Control.IsTabStopProperty.GetMetadata(typeof(UserControl)).DefaultValue);
Assert.IsFalse((bool)Control.IsTabStopProperty.GetMetadata(typeof(CustomUserControl)).DefaultValue);
Assert.IsTrue((bool)Control.IsTabStopProperty.GetMetadata(typeof(CustomControl)).DefaultValue); // fails
}
}
```

### Expected behavior

The last assert should pass

### Screenshots

_No response_

### NuGet package version

None

### Windows version

_No response_

### Additional context

_No response_

Start from the DependencyProperty.GetMetadata entry point and reproduce the failure with the CustomControl and CustomUserControl types shown in the issue. Compare the returned default values for Control and CustomControl, then add coverage for the listed assertions so the final CustomControl assertion passes.

Written by the indexing model from the issue text.