Migrate WinForms sample projects to .NET 8

[Copilot]

Migrate WinForms sample projects to .NET 8

Completed:

• Converted all WinForms projects to SDK-style .NET 8 format
• Removed non-existent OPCFoundation.NetStandard.Opc.Ua.Quickstarts.Servers package reference
• Created ReferenceServer.cs class
• Added HandleException backward-compatible 2-parameter overload in ClientUtils and ExceptionDlg
• Suppressed CA1416 platform compatibility warnings for Windows-only projects
• Fixed UserNamePasswordDlg byte[]/string type conversion
• Fixed X509AuthorityKeyIdentifierExtension ambiguous reference
• Fixed SelectNodeDlg.ShowDialogAsync call

In Progress:

• Fix remaining 36 API compatibility errors in ClientControls.Net4
  • Missing ClientUtils.SelectEndpoint, GetAttributeDisplayText, DiscoverServers methods
  • Session.Browse API signature changes
  • Session_KeepAlive delegate signature changes
  • Various ShowDialog overload changes

Build Status:

• 36 errors remaining (down from 110)
• ~100 warnings (down from 4000+ after suppressing CA1416)

Original prompt

Please update all winforms sample projects to net core.
Resolve all build errors.

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[romanett]

@copilot please fix warnings and errors