refactor(@angular/build): update private exports to expose Diagnostic… #2553

Job	Run time
list	23s
workflow (devkit-core-tests-rerun)	1m 22s
workflow (modules-builder-tests)	1m 48s
workflow (build-unit-tests)	2m 24s
workflow (build-cli)	1m 39s
workflow (devkit-core-tests)	1m 16s
	8m 52s

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