Split Build job into Build Packages and Build rest of artifacts

[scbedd]

Resolves #30038

Job layout before this change

Build
  -> Analyze
  -> PythonVersionX+PlatformY
  -> PythonVersionX+PlatformY
  -> ..

Where Build contains Create wheel/sdist, Create APIStub, Create docs.

Job layout after this change

Build (wheel/sdist)
  -> Build Extended (Docs, APIStubGen)
  -> Analyze
  -> PythonVersionX+PlatformY
  -> PythonVersionX+PlatformY
  -> ..

Two primary benefits after this change:

1. Tests will start faster as we won't be waiting for more than what is actually necessary to properly invoke those jobs. (we only actually need the whl/sdist, the rest can run and publish separately.)
2. This also really simplifies implementation of Enable non-universal wheel assembly #28211 as we no longer need to condition the apistubgen and docs steps to only run on the ubuntu agent!

For core, we start testing 12 minutes earlier due to this change. Packages like storage or ml will heavily benefit as well!

@kdestin initially raised this as a possibility, and I'm super happy with how it turned out. Thanks Kevin!

[mccoyp]

LGTM! This is great idea @kdestin, and thanks @scbedd for the implementation!

[scbedd]

I had a chat with @praveenkuttappan to verify.

This PR is not ready to merge as-is. We broke APIStubGen. Before, the step would inject a json output for the package in the packages artifact alongside the wheel/sdist.

<artifact staging root>/
    azure-core/
        azure-core.whl
        azure-core.zip
        azure-core_python.json

but now that we don't run APIStubGen as part of the assembly of the packages artifact, we need to pull from a different place when we run the APIStubGen verify step in Analyze.

To address this, we will make Analyze job depend on Build Extended (which will need to publish this APIStubGen artifact) and download the artifact from that job instead of Build.

[scbedd]

I think this PR is ready to go in.

However, I'm going to wait for @praveenkuttappan to return and do a final check.

[scbedd]

/azp run python - core - ci

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[scbedd]

/azp run python - core - ci

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[azure-sdk]

API change check

APIView has identified API level changes in this PR and created following API reviews.

azure-template

[scbedd]

/check-enforcer evaluate

[scbedd]

/check-enforcer evaluate