Add extension method for JsonSerializerOptions.GetTypeInfo

[agocke]

Fixes #118468

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[Copilot]

Pull Request Overview

This PR adds generic overloads for the GetTypeInfo and TryGetTypeInfo methods in JsonSerializerOptions to provide type-safe alternatives that return JsonTypeInfo<T> instead of the base JsonTypeInfo type. This enhancement improves the developer experience by eliminating the need for manual casting when working with strongly-typed JSON serialization metadata.

Key changes:

• Added GetTypeInfo<T>() generic method that returns JsonTypeInfo<T>
• Added TryGetTypeInfo<T>() generic method with strongly-typed output parameter
• Updated the reference assembly to include the new method signatures

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.Caching.cs	Implementation of generic GetTypeInfo<T>() and TryGetTypeInfo<T>() methods
src/libraries/System.Text.Json/ref/System.Text.Json.cs	Reference assembly updates to expose the new generic method signatures

[eiriktsarpalis]

LGTM, but could you also add a couple of rudimentary unit tests?

[agocke]

Note; I noticed that there was a duplicate implementation of this pattern in JsonSerializerContext. I'd like to fix both of them together, so I'll prototype this and present an updated API change.

[eiriktsarpalis]

Note; I noticed that there was a duplicate implementation of this pattern in JsonSerializerContext. I'd like to fix both of them together, so I'll prototype this and present an updated API change.

I don't think that would be strictly necessary for JSC. Source generated instances already expose strongly typed JTOs as static properties.

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[eiriktsarpalis]

@agocke are there any other changes you were planning to make before putting this PR out of draft?

[agocke]

I need to make sure I caught everything and that all tests pass.