Add a "status" API to DiagnosticContext, overhaul Downloads console output #1867

# to view logs

Job	Run time
json-schema	1s
format	1s
builds / build (windows-2022, windows-ci)	20m 3s
builds / build (ubuntu-20.04, linux-ci)	4m 45s
builds / build (macos-13, macos-ci)	1s
	24m 51s

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