Use new Helix API endpoint to fetch job results SAS token when downloading results

[simonrozsival]

There is a new endpoint in Helix API that allows fetching the results URI and a short-lived SAS token for read access to the results (see https://helix.dot.net/swagger/ui/index.html#/Job/Job_Results). The Microsoft.DotNet.Helix code should use this new endpoint in DownloadFromResultsContainer instead of relying on the SAS token returned in the new job response JSON.

This is follow-up to internal work items https://dev.azure.com/dnceng/internal/_workitems/edit/6933 and https://dev.azure.com/dnceng/internal/_workitems/edit/6937/