Libraries live live ci

[safern]

Not yet ready. Haven't even tested it.

cc: @jashook@sbomer

[jashook]

/cc @trylek

[trylek]

Overall looks good as a checkpoint even though I probably need for the change to expand a bit further to see more clearly the live live support unfold. In particular, for "live-live libraries CI sub-pipeline" (as standalone live live libraries CI pipeline doesn't make sense to me) I would expect the most important bit to be a way to propagate the location of live-live built System.Private.Corelib to use for building CoreFX / libraries and I don't yet see that.

On top of that, I was under the impression that we discussed maximizing reuse of YAML code between "subrepo pipelines" and the "live-live global pipeline" and I don't see any of that, I see just some new YAML getting added without any relationship to the existing pipelines / scripts.

[safern]

Overall looks good as a checkpoint even though I probably need for the change to expand a bit further to see more clearly the live live support unfold.

Yeah. This was just like the first progress that I made on Friday and this isn't even close to the design we discussed but it starts getting corefx's build logic to get closer to it and to be able to use xplat and platform matrix templates. The first step was to separate the build and tests steps as right now we're building sources and tests as part of the same step and build, but yeah, what you describe is the plan forward! Thanks for taking a look and sharing your thoughts, really valuable.