Use new HelixAPI /job/{job}/results endpoint

[simonrozsival]

Closes #15229

Instead of relying on the SAS token returned in the new job response JSON, this PR uses the new Helix API endpoint to fetch the results URI and a short-lived SAS token for read access to the results.

To double check:

• The right tests are in and the right validation has happened. Guidance: https://github.com/dotnet/arcade/blob/main/Documentation/Validation.md

[chcosta]

I wasn't able to get a repro set up to verify these changes myself. Theoretically, the code looks good to me. I added one nit.

[chcosta]

nit: I see this is only called in not null scenarios, but it still feels like a null check should occur in this method just in case someone else tries to consume this or someone tries to refactor the calling code and the check gets lost.

[simonrozsival]

The whole code generator is broken currently, and its outputs don't match the HTTP client code exactly. I had to make several more changes to get it to produce reasonable code (e.g., the generator doesn't add licensing comments at the start of every file).

My understanding is that the API surface doesn't change that often anymore and making the generator more robust isn't a high priority at the moment. I only committed this change because it is necessary to make the new API surface work with the generated code and somebody might find it useful if the ever need to actually fix the code generator. I'd rather avoid making any further changes to the generator in this PR.