fix(@angular/build): ensure locale base href retains leading slash (#… #2646

Job	Run time
list	25s
workflow (build-cli)	1m 30s
workflow (devkit-core-tests-rerun)	1m 30s
workflow (devkit-core-tests)	1m 19s
workflow (modules-builder-tests)	1m 51s
workflow (build-unit-tests)	2m 35s
	9m 10s

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