Mvc.Api.Analyzers should treat `IResult` types correctly

[brunolins16]

A support for IResults types in MVC Action controller is going to be added by #40710, however Mvc.Api.Analyzers still treat IResult returned instances as user defined Model, that basically means an OkResult (HTTP Status Code: 200) and might suggest the adding of incorrect Produces* attributes or incorrect warnings.

Relevant code: https://github.com/dotnet/aspnetcore/blob/main/src/Mvc/Mvc.Api.Analyzers/src/ActualApiResponseMetadataFactory.cs

Originally posted by @pranavkm in #40710 (comment)

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