Minimal APIs should return the standard media type for Problem Details responses #36557
Description
Minimal APIs that return the result of calling Microsoft.AspNetCore.Http.Results.ValidationProblem get a response media type of application/validationproblem+json which is not compliant with the RFC7807 spec that they're based on. The media type should be application/problem+json.
MVC has the same incorrect behavior but has since it was introduced in 2.x (see #36560).
We should fix this behavior in .NET 6.0 before final release.