refactor(@schematics/angular): use `generateFromFiles` helper in more… #851

Job	Run time
list	33s
workflow (build-cli)	1m 26s
workflow (modules-builder-tests)	1m 41s
workflow (devkit-core-tests)	1m 19s
workflow (devkit-core-tests-rerun)	1m 25s
workflow (build-unit-tests)	2m 31s
	8m 55s

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