Migrate remaining WPF legacy snippets

[adegeo]

Summary

Handling the issue in two steps:

• Migrate the code and verify the published pages and build.
• Delete the old code.

Fixes #2264

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Internal previews

📄 File	🔗 Preview link
dotnet-desktop-guide/wpf/security-wpf.md	dotnet-desktop-guide/wpf/security-wpf
dotnet-desktop-guide/wpf/wpf-partial-trust-security.md	dotnet-desktop-guide/wpf/wpf-partial-trust-security
dotnet-desktop-guide/wpf/wpf-security-strategy-platform-security.md	dotnet-desktop-guide/wpf/wpf-security-strategy-platform-security

[Copilot]

Pull request overview

This PR migrates remaining legacy WPF snippet references (from ~/samples/snippets/...) into per-article ./snippets/... folders, aligning snippet usage with the repo’s current :::code pattern and unblocking follow-up deletion of the old snippets folder (Fixes #2264).

Changes:

• Updated three WPF security articles to reference local snippet files via :::code ... source=... id=....
• Added new per-article snippet projects and source files for WPF platform security and partial-trust security examples (C# and VB).
• Added a new WPF security-wpf snippet set demonstrating SandboxExternalContent usage in Frame and NavigationWindow.

Reviewed changes

Copilot reviewed 31 out of 33 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
dotnet-desktop-guide/wpf/wpf-security-strategy-platform-security.md	Switches legacy snippet includes to local :::code references.
dotnet-desktop-guide/wpf/wpf-partial-trust-security.md	Switches legacy snippet includes to local :::code references.
dotnet-desktop-guide/wpf/security-wpf.md	Replaces legacy XAML snippet includes with local :::code references and adjusts surrounding text.
dotnet-desktop-guide/wpf/snippets/wpf-security-strategy-platform-security/vb/WPFPlatformSecuritySnippet.vbproj	Adds VB project to build the platform-security snippet set.
dotnet-desktop-guide/wpf/snippets/wpf-security-strategy-platform-security/vb/Page1.xaml.vb	Adds VB code-behind snippet for permission assert example.
dotnet-desktop-guide/wpf/snippets/wpf-security-strategy-platform-security/vb/Page1.xaml	Adds VB Page XAML used by the snippet project.
dotnet-desktop-guide/wpf/snippets/wpf-security-strategy-platform-security/vb/Application.xaml	Adds VB application definition for the snippet project.
dotnet-desktop-guide/wpf/snippets/wpf-security-strategy-platform-security/csharp/WPFPlatformSecuritySnippet.csproj	Adds C# project to build the platform-security snippet set.
dotnet-desktop-guide/wpf/snippets/wpf-security-strategy-platform-security/csharp/Page1.xaml.cs	Adds C# code-behind snippet for permission assert example.
dotnet-desktop-guide/wpf/snippets/wpf-security-strategy-platform-security/csharp/Page1.xaml	Adds C# Page XAML used by the snippet project.
dotnet-desktop-guide/wpf/snippets/wpf-security-strategy-platform-security/csharp/App.xaml	Adds C# application definition for the snippet project.
dotnet-desktop-guide/wpf/snippets/wpf-partial-trust-security/vb/WpfPartialTrustSecurity.vbproj	Adds VB project to build the partial-trust snippet set.
dotnet-desktop-guide/wpf/snippets/wpf-partial-trust-security/vb/Page1.xaml.vb	Adds VB page code-behind for the snippet project.
dotnet-desktop-guide/wpf/snippets/wpf-partial-trust-security/vb/Page1.xaml	Adds VB Page XAML used by the snippet project.
dotnet-desktop-guide/wpf/snippets/wpf-partial-trust-security/vb/FileHandlingGraceful.vb	Adds VB “graceful degradation” snippet implementation.
dotnet-desktop-guide/wpf/snippets/wpf-partial-trust-security/vb/FileHandling.vb	Adds VB permission-detection snippet implementation.
dotnet-desktop-guide/wpf/snippets/wpf-partial-trust-security/vb/Application.xaml	Adds VB application definition for the snippet project.
dotnet-desktop-guide/wpf/snippets/wpf-partial-trust-security/csharp/WpfPartialTrustSecurity.csproj	Adds C# project to build the partial-trust snippet set.
dotnet-desktop-guide/wpf/snippets/wpf-partial-trust-security/csharp/Page1.xaml.cs	Adds C# page code-behind for the snippet project.
dotnet-desktop-guide/wpf/snippets/wpf-partial-trust-security/csharp/Page1.xaml	Adds C# Page XAML used by the snippet project.
dotnet-desktop-guide/wpf/snippets/wpf-partial-trust-security/csharp/FileHandlingGraceful.cs	Adds C# “graceful degradation” snippet implementation.
dotnet-desktop-guide/wpf/snippets/wpf-partial-trust-security/csharp/FileHandling.cs	Adds C# permission-detection snippet implementation.
dotnet-desktop-guide/wpf/snippets/wpf-partial-trust-security/csharp/App.xaml	Adds C# application definition for the snippet project.
dotnet-desktop-guide/wpf/snippets/security-wpf/csharp/SecurityWpf.csproj	Adds C# WPF snippet project for security-wpf.md examples.
dotnet-desktop-guide/wpf/snippets/security-wpf/csharp/NavigationWindowExample.xaml	Adds XAML snippet for sandboxed NavigationWindow external content.
dotnet-desktop-guide/wpf/snippets/security-wpf/csharp/MainWindow.xaml.cs	Adds code-behind for the WPF snippet project main window.
dotnet-desktop-guide/wpf/snippets/security-wpf/csharp/MainWindow.xaml	Adds XAML snippet for sandboxed Frame external content.
dotnet-desktop-guide/wpf/snippets/security-wpf/csharp/ExternalContentPage.xaml	Adds external content page referenced by the sandboxing examples.
dotnet-desktop-guide/wpf/snippets/security-wpf/csharp/AssemblyInfo.cs	Adds WPF theme info assembly attribute.
dotnet-desktop-guide/wpf/snippets/security-wpf/csharp/App.xaml.cs	Adds WPF application class for the snippet project.
dotnet-desktop-guide/wpf/snippets/security-wpf/csharp/App.xaml	Adds WPF application definition for the snippet project.

[BillWagner]

This LGTM. Let's