Consider consolidating the SB pipelines with the UB pipelines

[MichaelSimons]

Current the Microsoft UB pipeline and SB pipeline are separate pipelines that share a common implementation. Once Microsoft starts shipping it's release from the VMR, it would be beneficial to combine these pipelines.

Benefits:

1. The Microsoft build cannot pass if source-build is failing. This is to say this will help ensure source-build works for every Microsoft build.
2. When testing source-build, the scenario-tests need access to the Microsoft packages. When testing from a customer's perspective, source-build scenarios require the packages Microsoft publishes. This is to say source-build needs access to the just built Microsoft packages. This also implies that the source-build tests should run as part of the validation phase and not part of the build phase as the source-build and Microsoft builds would happen concurrently.

One downside to this approach is currently it is easy for the source-build team to monitor their builds are passing. With this change that becomes a little more difficult. Tooling can address this issue.

[MichaelSimons]

cc @ViktorHofer, @mmitche

[ViktorHofer]

Love the first point. It's true that one should not ship with the other failing.

I think this is the right and logical step forward and will make the unified build pipeline truely unified.

Unrelated to this issue, but scenario-tests when running locally (-dev) or in PRs (-ci) might need to run with the just built source build packages as an approximation.

[MichaelSimons]

Assigning to Matt at this is being done as part of the Official Build Id work