Rewrite covariance/contravariance definitions to be user-focused

[Copilot]

• Rewrite the covariance, contravariance, and invariance definitions to be more concrete and user-focused
• Use the "where X type is permitted, you can do Y" framing as suggested in the issue
• Address review: use "generic type argument" instead of "generic type parameters" for substitution context
• Address review: reorder definitions to start with invariant (baseline: no substitution), then covariant, then contravariant
• Update frontmatter with current date and ai-usage: ai-assisted
• Review and validate changes

Original prompt

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This section details on the original issue you should resolve

<issue_title>can be clearer</issue_title>
<issue_description>The article says

Covariance
Enables you to use a more derived type than originally specified.
Contravariance
Enables you to use a more generic (less derived) type than originally specified.

Rather than talking about covariance and contravariance in general terms, I think would be more effective to start by using the terms covariant and contravariant concretely. Something like,

Where a covariant type is permitted, you can use a more derived type.
Where a contravariant type is permitted, you can use a more generic type.
Where an invariant type is required, you cannot use either a more derived or a more generic type.

The general terms are more appropriate to theoretical and implementation discussions, not so much for how to use language and API features. So I think they should be used very sparingly on this page.

I bet this page would be a lot better after some user testing. Lots of people have trouble with these terms.

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Document Details

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

• ID: 74e47b2d-ee75-bd2e-4857-7704af641a2a
• Version Independent ID: 8055442b-8ecf-e869-3e48-a5c4ee5207a1
• Content: Covariance and Contravariance in Generics
• Content Source: docs/standard/generics/covariance-and-contravariance.md
• Product: dotnet
• Technology: dotnet-standard
• GitHub Login: @adegeo
• Microsoft Alias: adegeo</issue_description>

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

@adegeo Thank you for opening this issue. I'll add it to the backlog. If you would like to contribute, you can submit a fix by editing the original article. Click on the **Content Source** link at the bottom of your original comment. To learn how to edit, see the [Editing files in a repository](https://help.github.com/articles/editing-files-in-your-repository) article from GitHub.

Thanks again!</comment_new>

• Fixes can be clearer #19285

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docs/standard/generics/covariance-and-contravariance.md	Covariance and contravariance in generics

[BillWagner]

Hi @copilot

A couple things to change before this is ready.

[BillWagner]

This is now ready for final review.

[Copilot]

Pull request overview

Updates the introductory definitions in the generics variance article to be more concrete and user-focused, aligning the framing with “where X is permitted, you can do Y,” and updating metadata to reflect AI-assisted edits.

Changes:

• Rewrites the opening explanation of covariance, contravariance, and invariance with clearer, example-driven definitions.
• Reorders the definitions to start with invariance, then covariance, then contravariance.
• Updates frontmatter (ms.date) and adds ai-usage: ai-assisted.