fix(@angular-devkit/build-angular): conditionally provide Zone.js cha… #2650

Job	Run time
list	24s
workflow (build-unit-tests)	2m 31s
workflow (modules-builder-tests)	1m 49s
workflow (build-cli)	1m 42s
workflow (devkit-core-tests-rerun)	1m 25s
workflow (devkit-core-tests)	1m 27s
	9m 18s

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