Add support for validation jobs to `sync.ts`, and refactor #2935

Job	Run time
Upload debug artifacts (stable-v2.20.3)	5m 49s
Upload debug artifacts (default)	6m 0s
Upload debug artifacts (linked)	5m 25s
Upload debug artifacts (nightly-latest)	5m 50s
Download and check debug artifacts	12s
	23m 16s

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