refactor(@angular/build): improve Vitest configuration merging #2384

Job	Run time
list	20s
workflow (modules-builder-tests)	1m 43s
workflow (build-unit-tests)	2m 29s
workflow (build-cli)	1m 36s
workflow (devkit-core-tests)	1m 16s
workflow (devkit-core-tests-rerun)	1m 17s
	8m 41s

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