Fix outdated statement about record types always being reference types

[Copilot]

Summary

Since C# 10, record struct allows records to be value types, making the statement "types defined with the record keyword are reference types" inaccurate.

Changes:

• Line 74: Clarified struct or record struct → value types; class or record class → reference types
• Line 127: Changed record to record class in reference type definition

Fixes #49949

Original prompt

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This section details on the original issue you should resolve

<issue_title>Outdated statement about record types always being reference types</issue_title>
<issue_description>### Describe the issue or suggestion

In the [C# Fundamentals / Type System / Overview] (https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/types/#:~:text=Types%20that%20you%20define%20by%20using%20the%20class%20or%20record%20keyword%20are%20reference%20types.) the documentation says: "Types that you define by using the class or record keyword are reference types.". However, since C# 10 introduced record struct, this statement is no longer accurate.
Thanks for maintaining these excellent docs — just a small fix to keep them up to date!

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Document Details

⚠ Do not edit this section. It is required for learn.microsoft.com ➟ GitHub issue linking.

• ID: 1991c89a-9728-ea31-a999-79b3cb331372
• Version Independent ID: 9aa4f01b-a5a0-3cb1-3c22-db333c0d9f11
• Platform ID: 30e147af-ed76-bf1c-6227-a0627346a70b
• Content: Learn the fundamentals of the C# type system - C#
• Content Source: docs/csharp/fundamentals/types/index.md
• Service: dotnet-csharp
• Sub-service: fundamentals
• GitHub Login: @BillWagner
• Microsoft Alias: wiwagn</issue_description>

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

• Fixes Outdated statement about record types always being reference types #49449

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Internal previews

📄 File	🔗 Preview link
docs/csharp/fundamentals/types/index.md	The C# type system

[Copilot]

Pull Request Overview

This PR updates outdated documentation about C# record types to reflect the introduction of record struct in C# 10. Previously, the documentation incorrectly stated that all records are reference types, but record struct allows records to be value types.

Key Changes:

• Updated line 74 to clarify that both struct and record struct create value types, while class and record class create reference types
• Updated line 127 to specify record class instead of just record when defining reference types

[BillWagner]

This is fine, with one clarifying change.