refactor(@angular/build): create shared utility for external metadata #9139

Job	Run time
lint	2m 17s
build	4m 8s
build-e2e-windows	4m 29s
Browser Compatibility Tests	19s
test	18s
publish-snapshots	19s
e2e-windows	1s
e2e-snapshots	1s
e2e	1s
e2e-package-managers	1s
	11m 54s

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