Update documentation and guides related to WinForms Accessibility

**.NET Core Version:**

.NET Core SDK (reflecting any global.json):
Version: 5.0.100-alpha.1.20073.10
Commit: 29f4d693a9

Runtime Environment:
OS Name: Windows
OS Version: 10.0.18363
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\5.0.100-alpha1-05536\

**Have you experienced this same bug with .NET Framework?:**
Yes

**Problem description:**
WinForms documentation and guides do not fully describe the steps and options about setting accessibility properties:
* https://github.com/dotnet/docs/blob/live/docs/framework/winforms/controls/providing-accessibility-information-for-controls-on-a-windows-form.md
* https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.control.accessiblename?view=netframework-4.8
* https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.control.accessibledefaultactiondescription?view=netframework-4.8

Additionally, the example from [`AccessibleObject`](https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.accessibleobject) page doesn't show how to make screen readers announce changes in control's state. and therefore might need to be revisited.

**Expected behavior:**
Documentation and guides should be descriptive to allow app developers to implement accessible applications using WinForms controls.

**Minimal repro:**
Create WinForms app, add several WinForms controls to the form, try to get information how to set up accessibility properties to make the application fully accessible.
There is no default information except the `AccessibleName` has default value 'null'.