refactor(@angular/build): provide private factory API for internal co… #650

Job	Run time
list	28s
workflow (modules-builder-tests)	35s
workflow (build-cli)	26s
workflow (devkit-core-tests-rerun)	28s
workflow (build-unit-tests)	32s
workflow (devkit-core-tests)	26s
	2m 55s

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