refactor(@angular/build): update private exports to expose Diagnostic… #2554

Job	Run time
list	23s
workflow (devkit-core-tests-rerun)	1m 29s
workflow (devkit-core-tests)	1m 21s
workflow (build-unit-tests)	2m 26s
workflow (modules-builder-tests)	1m 58s
workflow (build-cli)	1m 35s
	9m 12s

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