Switch to live built dependencies

[ViktorHofer]

By default cross sub-repository dependencies are resolved live. The existing contracts (nuget feeds) will be removed. Mixed build configurations between the sub-repositories will be supported, e.g. to consume a Release build of CoreClr from within libraries.

Goals

• Mixed build configurations are supported.
• Arcade extension points for publishing and signing are converged: Signing.props and Publishing.props.
• The NETCoreApp shared framework is produced from the live built assets from CoreFx, CoreClr and Core-Setup.

Open PRs:

• Libraries live live ci #71
• Local Live live builds #55

cc @dotnet/runtime-infrastructure

[ViktorHofer]

ETA: First week of December.

[ViktorHofer]

Updated the ETA.

[ViktorHofer]

Closing as the live built is finished. Signed builds are tracked by a different issue.