fix(@angular-devkit/build-angular): conditionally provide Zone.js cha… #1397

Job	Run time
list	24s
workflow (modules-builder-tests)	24s
workflow (build-cli)	22s
workflow (devkit-core-tests-rerun)	25s
workflow (build-unit-tests)	21s
workflow (devkit-core-tests)	24s
	2m 20s

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