Set content-type to application/problem+json for generic TypedResults with T=ProblemDetails

[mikekistler]

Is there an existing issue for this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe the problem.

Currently when an endpoint returns a generic TypedResults with T=ProblemDetails, such as NotFound<ProblemDetails>,
the content-type is set to application/json instead of application/problem+json.

The endpoint could set the content-type manually, but it would be nice if the framework could do this automatically.

Note that the generated OpenAPI document currently shows the response as application/json, which is correct
as long as the endpoint does not set the content-type manually.

Describe the solution you'd like

Set the content-type application/problem+json for TypedResults with T=ProblemDetails and reflect this in the OpenAPI document.

Additional context

No response

[mikekistler]

Repro at https://github.com/mikekistler/aspnetcore-issue-repros/ProblemDetails.