refactor(@angular/build): provide private factory API for internal co… #1452

Job	Run time
list	27s
workflow (build-unit-tests)	2m 5s
workflow (devkit-core-tests)	1m 12s
workflow (modules-builder-tests)	1m 46s
workflow (build-cli)	1m 36s
workflow (devkit-core-tests-rerun)	1m 10s
	8m 16s

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