refactor(@angular/build): improve Vitest configuration merging #2385

Job	Run time
list	27s
workflow (modules-builder-tests)	1m 51s
workflow (devkit-core-tests-rerun)	1m 24s
workflow (build-cli)	1m 41s
workflow (build-unit-tests)	2m 26s
workflow (devkit-core-tests)	1m 27s
	9m 16s

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