fix(@angular/build): normalize `allowedHosts` in dev-server #2756

Job	Run time
lint	2m 7s
build	17s
build-e2e-windows	21s
Browser Compatibility Tests	0s
test	0s
publish-snapshots	0s
e2e-package-managers	0s
e2e-snapshots	0s
e2e	0s
e2e-windows	0s
	2m 45s

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