'StatusBar' class could not be found in System.Windows.Forms

[John-Qiao]

• .NET Core Version: 5.0.100-preview.1.20112.13

• Have you experienced this same bug with .NET Framework?: No

Problem description:
Cannot create the System.Windows.Forms.StatusBar class object in .NET Core 5.0 project.

More info:

1. This issue cannot repro in the latest NET Core 3.1 project.
2. The System.Windows.Forms.StatusBarPanel class object cannot be created too.

Expected behavior:
Can create the System.Windows.Forms.StatusBar class object in .NET Core 5.0 project successfully.

Minimal repro:

1. Create a Winforms Core application.
2. Open Form1.cs file and add the following code in Form1 class.
   StatusBar ss = new StatusBar();
3. Build the application.

[John-Qiao]

That's by design and described in there: dotnet/docs#17008

[RussKie]

Relates to #2798