Add generic ConsumesAttribute<T>

[campersau]

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Add a generic ConsumesAttribute

Description

Adds ConsumesAttribute<T>, a generic variant of ConsumesAttribute that lets the request type be specified as a type parameter instead of through the Type requestType constructor overload, mirroring the existing ProducesResponseTypeAttribute<T> pattern:

[Consumes<Todo>("application/x-www-form-urlencoded")]
async Task<IResult> AddTodo(Todo todo, TodoDb db)

ConsumesAttribute<T> inherits from ConsumesAttribute and forwards to the existing ConsumesAttribute(Type requestType, string contentType, params string[] otherContentTypes) constructor with typeof(T). It automatically picks up the base class's [AttributeUsage(Class | Method)] as well as IAcceptsMetadata/IConsumesActionConstraint behavior, so no additional wiring is needed for either MVC controllers or minimal API endpoints.

No new tests were added. Instead, existing tests that already exercised ConsumesAttribute with an explicit request type were updated to use the new Consumes<T> syntax, which confirms the generic form behaves identically to the non-generic one:

• EndpointMetadataApiDescriptionProviderTest
• OpenApiDocumentServiceTests.RequestBody
• OpenApiGeneratorTests

Fixes #67701

[dotnet-policy-service]

Thanks for your PR, @campersau. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[Youssef1313]

Thanks for the contribution @campersau.

We will need to review the API proposal first before moving forward. So, marking request changes until the API is reviewed/approved.

[gfoidl]

marking request changes

@Youssef1313 can you make this PR a draft also? (I don't have rights for this).