Consolidating the CI workflows into a single postsubmit.yml broke the
individual platform status badges in the README, as GitHub Actions
only supports status badges at the workflow level, not the job level.
Added shadow workflows (e.g., status-android.yml) that trigger on
the completion of the main "Postsubmit CI" workflow. These scripts
query the GitHub Actions API to determine the success or failure of
their respective job (e.g., build-android) and reflect that status.
Updated the README to point to these new workflow badges.
Powei Feng
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