Add a "status" API to DiagnosticContext, overhaul Downloads console output #1870

Job	Run time
json-schema	1m 3s
json-schema	1m 3s
format	2m 38s
format	2m 38s
builds / build (windows-2022, windows-ci)	20m 7s
builds / build (windows-2022, windows-ci)	20m 7s
builds / build (ubuntu-20.04, linux-ci)	1s
builds / build (ubuntu-20.04, linux-ci)	9m 32s
builds / build (macos-13, macos-ci)	15m 18s
builds / build (macos-13, macos-ci)	15m 18s
	1h 27m 45s

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