Update tutorials and program guide for modern extensions

[BillWagner]

Contributes to #45758

Commit history: (It may be easiest to review commit-by-commit)

1. Update the sample code and snippet tags for the LINQ tutorial. The code was several versions old. I think this hasn't been freshened with new concepts since .NET 6
2. First pass edit on LINQ tutorial.
3. Second pass edit on LINQ tutorial.
4. Edit extensions in programming guide, classes and struct section.
5. Finish other edits on programming guide.

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Internal previews

📄 File	🔗 Preview link
docs/csharp/programming-guide/classes-and-structs/how-to-create-a-new-method-for-an-enumeration.md	How to create a new method for an enumeration (C# Programming Guide)
docs/csharp/programming-guide/classes-and-structs/how-to-use-implicitly-typed-local-variables-and-arrays-in-a-query-expression.md	"How to use implicitly typed local variables and arrays in a query expression"
docs/csharp/programming-guide/generics/constraints-on-type-parameters.md	Constraints on type parameters (C# Programming Guide)
docs/csharp/toc.yml	Taken from https://github.com/dotnet/roslyn/wiki/Samples-and-Walkthroughs
docs/csharp/tutorials/working-with-linq.md	docs/csharp/tutorials/working-with-linq

[BillWagner]

I marked this as ready, and changed from "fixes" to "contributes to". The one folder remaining is the LINQ section, which will have quite a few changes. Splitting to make reviews a bit easier.

[Copilot]

Pull request overview

This pull request modernizes the LINQ tutorial and programming guide for C# extension members. The primary focus is updating the sample code to use the modern extension syntax introduced in C# 14, along with editorial improvements to align with documentation style guidelines.

Key changes:

• Updates the LINQ tutorial with modernized extension member syntax and improved editorial clarity
• Reorganizes the table of contents to elevate "Extension members" to a top-level section
• Updates project files to target .NET 10.0 (net10.0)

Reviewed changes

Copilot reviewed 16 out of 17 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
docs/csharp/tutorials/working-with-linq.md	Updated LINQ tutorial with editorial improvements, modernized terminology, and corrected date/metadata
docs/csharp/tutorials/snippets/console-linq/Program.cs	New main program file using modern extension syntax and updated enum-based card deck
docs/csharp/tutorials/snippets/console-linq/extensions.cs	Refactored to use modern extension container syntax instead of traditional static extension methods
docs/csharp/tutorials/snippets/console-linq/InterimSteps.cs	New file containing tutorial step-by-step code snippets for progressive learning
docs/csharp/tutorials/snippets/console-linq/playingcard.cs	Modernized to use record type with sealed modifier
docs/csharp/tutorials/snippets/console-linq/README.md	New README documenting the sample project
docs/csharp/tutorials/snippets/console-linq/LInqFaroShuffle.csproj	Updated to target net10.0 with ImplicitUsings enabled
docs/csharp/programming-guide/generics/snippets/GenericWhereConstraints.cs	Updated extension method examples to use modern extension syntax
docs/csharp/programming-guide/generics/snippets/generics.csproj	Updated to target net10.0
docs/csharp/programming-guide/classes-and-structs/snippets/how-to-implement-and-call-a-custom-extension-method/Program.cs	Refactored to demonstrate modern extension member syntax
docs/csharp/programming-guide/classes-and-structs/snippets/how-to-implement-and-call-a-custom-extension-method/how-to-implement-and-call-a-custom-extension-method.csproj	Updated to target net10.0
docs/csharp/programming-guide/classes-and-structs/how-to-use-implicitly-typed-local-variables-and-arrays-in-a-query-expression.md	Updated cross-reference from "Extension Methods" to "Extension members"
docs/csharp/programming-guide/classes-and-structs/how-to-create-a-new-method-for-an-enumeration.md	Updated date metadata
docs/csharp/programming-guide/generics/constraints-on-type-parameters.md	Updated date metadata
docs/csharp/toc.yml	Reorganized to promote "Extension members" to a top-level section under "Classes, Structs, and Records"
samples/snippets/csharp/getting-started/console-linq/playingcard.cs	Removed old file (replaced by tutorial snippets version)
samples/snippets/csharp/getting-started/console-linq/Program.cs	Removed old file (replaced by tutorial snippets version)

[BillWagner]

Talk back to copilot