refactor(@schematics/angular): use `generateFromFiles` helper in even… #864

Job	Run time
list	24s
workflow (devkit-core-tests)	1m 17s
workflow (build-cli)	1m 27s
workflow (devkit-core-tests-rerun)	1m 14s
workflow (build-unit-tests)	2m 20s
workflow (modules-builder-tests)	1m 54s
	8m 36s

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