fix(@angular/build): setup unit-test polyfills before TestBed init #1106

Job	Run time
list	22s
workflow (devkit-core-tests-rerun)	1m 24s
workflow (modules-builder-tests)	1m 50s
workflow (build-cli)	1m 29s
workflow (build-unit-tests)	2m 20s
workflow (devkit-core-tests)	1m 23s
	8m 48s

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