Add support for diagnostic tags, and use them for `mergeDefaultSetupAndUserConfigs` #8438

Job	Run time
Ruby analysis (macos-latest, linked)	1m 0s
Ruby analysis (ubuntu-latest, linked)	41s
Ruby analysis (macos-latest, nightly-latest)	1m 1s
Ruby analysis (ubuntu-latest, default)	39s
Ruby analysis (ubuntu-latest, nightly-latest)	45s
Ruby analysis (macos-latest, default)	54s
	5m 0s

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