Convert `sync_back.py` to TypeScript #2816

Job	Run time
Upload debug artifacts (linked)	5m 54s
Upload debug artifacts (stable-v2.20.3)	5m 33s
Upload debug artifacts (nightly-latest)	5m 37s
Upload debug artifacts (default)	6m 22s
Download and check debug artifacts	9s
	23m 35s

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