- Removed duplication and unnecessary indirection from all suites testcfgs.
 - Introduced a more comprehensive context to cover both command context and other platform specific concerns.
 - Propagated above context to TestLoader to allow for test counting command execution on all platforms.
 - Wrapped original pool with another class to give it a new interface and allow injecting different implementations in the future.
 - Consolidated progress indicators under a single processor in the pipeline.
 - Consolidated result retention requirements calculation outside of pipeline chain.
 - Refactored LoaderProc and got it under tests.
 - Added some more tests for the standard runner.
 - Extracted BuildConfig class.


Bug: v8:12785
Change-Id: I87be040e91f792a983662bb5a10d55b36a14ea7f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3701595Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Liviu Rau <liviurau@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81770}