refactor(@angular/ssr): handle promise-like results from `loadChildre… #2083

Job	Run time
list	23s
workflow (build-unit-tests)	2m 9s
workflow (devkit-core-tests-rerun)	1m 22s
workflow (build-cli)	1m 49s
workflow (modules-builder-tests)	1m 46s
workflow (devkit-core-tests)	1m 26s
	8m 55s

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