Add file results documentation for Minimal APIs and controllers

[mikekistler]

Adds documentation for file result return values in ASP.NET Core, covering both Minimal APIs and controller-based APIs.

What's included

• File result types — TypedResults.File / ControllerBase.File() with byte[] and Stream
• OpenAPI support — Using Produces<Stream> for binary, Produces<string> for text
• Conditional requests — ETag and Last-Modified with 304 Not Modified
• Range requests — enableRangeProcessing for partial content (206) responses

Code examples reference snippets in dotnet/AspNetCore.Docs.Samples (PR: dotnet/AspNetCore.Docs.Samples#312).

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Internal previews

📄 File	🔗 Preview link
aspnetcore/fundamentals/minimal-apis/responses.md	aspnetcore/fundamentals/minimal-apis/responses

[wadepickett]

Great content. I found a few minor items, with suggestions inline.

For the build issue warning of missing code:
The article references ~/../AspNetCore.Docs.Samples/fundamentals/minimal-apis/FileResults/10.x/... but on main only fundamentals/minimal-apis/samples/ exists: The new FileResults/10.x/ folder is in PR #312 and hasn't been merged. It should be merged first.

[wadepickett]

Approved, but review suggestions I made for some minor items inline and merge PR #312 first so the code will be found when this content builds again.

[Youssef1313]

Is this where it's handled?

https://github.com/dotnet/aspnetcore/blob/ad2f14fdbc53a72f050070a473954ec0f1e3469d/src/OpenApi/src/Services/Schemas/OpenApiSchemaService.cs#L65-L68

Does that mean that FileContentHttpResult already works?

[mikekistler]

I believe FileContentResult, FileContentHttpResult, StreamContentResult, and StreamContentHttpResult were all added in .NET 11 and not backported to .NET 10. So only 'IFormFile, Stream, and PipeReader` will work in .NET 10.