Make ApiDescriptionActionData public

[tebeco]

(I have no idea if i took the proper branch, i started on 3.0, and i wonder if i should have took 3.1.0-preview1

Summary of the changes

• Make ApiDescriptionActionData public back

Addresses #14954 (suggested by @pranavkm / @mkArtakMSFT )
see domaindrivendev/Swashbuckle.AspNetCore#1316 (comment)

I have no idea if the scaffolding should change of if there's anything else to add on top of this

[pranavkm]

@tebeco could you cherry-pick your changes on the release/3.1 branch? 3.0 has already shipped and we can not add new APIs to it.

[tebeco]

@pranavkm , done

[pranavkm]

Thanks @tebeco. Could you also update the reference assembly in Microsoft.AspNetCore.Mvc.Core. See https://github.com/aspnet/AspNetCore/blob/master/docs/ReferenceAssemblies.md#when-changing-public-api

[tebeco]

out of curiousity, what is Helix :D ?

https://github.com/dotnet/arcade/tree/master/src/Microsoft.DotNet.Helix/Sdk ?

Should i worry about these build ? anything that i should do to fix it ?

[javiercn]

This looks good to me, @pranavkm for final sign-off. It's my understanding we want to take this.

[pranavkm]

Thanks @tebeco!