fix(@angular-devkit/build-angular): mark `InjectionToken` as pure for… #1956

Job	Run time
list	23s
workflow (build-cli)	1m 40s
workflow (devkit-core-tests)	1m 15s
workflow (devkit-core-tests-rerun)	1m 22s
workflow (modules-builder-tests)	1m 43s
workflow (build-unit-tests)	2m 20s
	8m 43s

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