Update GetHashCode implementations to use HashCode.Combine

[Copilot]

• Analyzed the codebase to find GetHashCode implementations using outdated patterns (XOR, Tuple) that should use HashCode.Combine
• Update xor2.cs (C#): Replace Tuple.Create(x, y).GetHashCode() with HashCode.Combine(x, y)
• Update xor2.vb (VB): Replace Tuple.Create(x, y).GetHashCode() with HashCode.Combine(x, y)
• Update xor2.fs (F#): Replace tuple hash with System.HashCode.Combine(x, y)
• Update system-object-gethashcode.md: Updated article text to recommend HashCode.Combine; removed version reference per reviewer suggestion; updated shift1 section to say "In .NET Framework" per reviewer suggestion
• Update equals2.cs (C#): Update Point2 and Point3D.GetHashCode to use HashCode.Combine
• Update equals2.vb (VB): Update Point1 and Point3D.GetHashCode to use HashCode.Combine
• Update equals2.fs (F#): Update Point and Point3D.GetHashCode to use HashCode.Combine
• Update C# covariance article: Update inline PersonComparer.GetHashCode to use HashCode.Combine
• Update VB covariance article: Update inline PersonComparer.GetHashCode to use HashCode.Combine
• Add missing Project.fsproj in F# Equals snippets folder to fix CI build
• Add missing Project.fsproj in F# GetHashCode snippets folder to fix CI build

Original prompt

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This section details on the original issue you should resolve

<issue_title>Review GetHashCode implementations</issue_title>
<issue_description>Starting with .NET Core 3.1, HashCode.Combine APIs existed and should be the recommended way to implement GetHashCode method.

This is one example where the new implementation can be used.

The same applies to dotnet-api-docs repo, should I open another issue there?

• Related to Use HashCode instead of manual hashcode combining runtime#33762
• this shouldn't touch any .NET Framework-specific code, or versions under .NET Core 3.1</issue_description>

Comments on the Issue (you are @copilot in this section)

@gewarren I think it's fine to track this in one place, even for the dotnet-api-docs repo.

• Fixes Review GetHashCode implementations #19575

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Internal previews

📄 File	🔗 Preview link
docs/csharp/programming-guide/concepts/covariance-contravariance/using-variance-in-interfaces-for-generic-collections.md	Using Variance in Interfaces for Generic Collections (C#)
docs/fundamentals/runtime-libraries/system-object-gethashcode.md	System.Object.GetHashCode method
docs/visual-basic/programming-guide/concepts/covariance-contravariance/using-variance-in-interfaces-for-generic-collections.md	Using Variance in Interfaces for Generic Collections (Visual Basic)

[BillWagner]

Tagging @T-Gro

Do you want the F# samples here to use HashCode.Combine? We recommend it for C# and VB. What's the F# community consensus here?

If not, I'll have Copilot reverse those changes.

[T-Gro]

In F# the need to do custom HashCode is quite rare, using the .Combine helpers to put together two hash codes is OK here.

[BillWagner]

With a couple suggestions, this is ready for final review

[BillWagner]

@copilot You need to add a basic fsproj file in the /docs/fundamentals/runtime-libraries/snippets/System/Object/Equals/fsharp folder.

That will fix the CI build.

[Copilot]

Pull request overview

Updates GetHashCode guidance and snippets across the docs repo to use System.HashCode.Combine instead of older, collision-prone or allocation-heavy patterns.

Changes:

• Replaces tuple-based hashing and shift/XOR patterns in GetHashCode examples with HashCode.Combine.
• Updates System.Object.GetHashCode article text to recommend HashCode.Combine and positions shift-and-wrap as a .NET Framework-era alternative.
• Simplifies PersonComparer.GetHashCode in C# and Visual Basic variance articles to use HashCode.Combine.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
docs/visual-basic/programming-guide/concepts/covariance-contravariance/using-variance-in-interfaces-for-generic-collections.md	Updates VB comparer hash logic to HashCode.Combine.
docs/fundamentals/runtime-libraries/system-object-gethashcode.md	Updates guidance to recommend HashCode.Combine and reframes shift-and-wrap for .NET Framework.
docs/fundamentals/runtime-libraries/snippets/System/Object/GetHashCode/vb/xor2.vb	Switches tuple hashing to HashCode.Combine and updates output note.
docs/fundamentals/runtime-libraries/snippets/System/Object/GetHashCode/fsharp/xor2.fs	Switches tuple hashing to HashCode.Combine and updates output note.
docs/fundamentals/runtime-libraries/snippets/System/Object/GetHashCode/csharp/xor2.cs	Switches tuple hashing to HashCode.Combine and updates output note.
docs/fundamentals/runtime-libraries/snippets/System/Object/Equals/vb/equals2.vb	Updates Point/Point3D hash logic to HashCode.Combine.
docs/fundamentals/runtime-libraries/snippets/System/Object/Equals/fsharp/equals2.fs	Updates Point/Point3D hash logic to HashCode.Combine.
docs/fundamentals/runtime-libraries/snippets/System/Object/Equals/csharp/equals2.cs	Updates Point/Point3D hash logic to HashCode.Combine.
docs/csharp/programming-guide/concepts/covariance-contravariance/using-variance-in-interfaces-for-generic-collections.md	Updates C# comparer hash logic to HashCode.Combine.

[Copilot]

@copilot You need to add a basic fsproj file in the /docs/fundamentals/runtime-libraries/snippets/System/Object/Equals/fsharp folder.

That will fix the CI build.

Added Project.fsproj in commit f13263e. The project includes all 8 .fs files in that folder and builds successfully.

[BillWagner]

@copilot One more fsproj file to add in this folder: docs/fundamentals/runtime-libraries/snippets/System/Object/GetHashCode/fsharp/

[Copilot]

@copilot One more fsproj file to add in this folder: docs/fundamentals/runtime-libraries/snippets/System/Object/GetHashCode/fsharp/

Added Project.fsproj for the GetHashCode/fsharp folder in commit 67ad368. It includes all 4 .fs files and builds successfully.