Basic support for overlay databases #3878

Job	Run time
Diagnostic export (ubuntu-latest, nightly-latest)	59s
Diagnostic export (ubuntu-latest, linked)	1m 2s
Diagnostic export (macos-latest, linked)	1m 38s
Diagnostic export (windows-latest, linked)	4m 35s
Diagnostic export (macos-latest, nightly-latest)	1m 18s
Diagnostic export (windows-latest, nightly-latest)	3m 44s
	13m 16s

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