refactor(@angular-devkit/schematics): support `isolatedDeclarations` … #2883

Job	Run time
list	22s
workflow (build-cli)	1m 50s
workflow (modules-builder-tests)	1m 57s
workflow (build-unit-tests)	2m 29s
workflow (devkit-core-tests-rerun)	1m 41s
workflow (devkit-core-tests)	1m 27s
	9m 46s

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