refactor(@angular/build): provide a default for the application index… #1449

Job	Run time
build	13s
lint	1m 57s
e2e_windows (windows-2025, 22, npm, 1)	1m 21s
e2e_windows (windows-2025, 22, npm, 0)	26s
e2e_windows (windows-2025, 22, esbuild, 3)	1m 6s
e2e_windows (windows-2025, 22, npm, 5)	46s
e2e_windows (windows-2025, 22, esbuild, 0)	1m 55s
e2e_windows (windows-2025, 22, esbuild, 1)	23s
e2e_windows (windows-2025, 22, esbuild, 2)	22s
e2e_windows (windows-2025, 22, esbuild, 5)	29s
e2e_windows (windows-2025, 22, esbuild, 4)	30s
e2e_windows (windows-2025, 22, npm, 4)	23s
e2e_windows (windows-2025, 22, npm, 3)	1m 19s
e2e_windows (windows-2025, 22, npm, 2)	36s
publish-snapshots	-1s
test	-1s
e2e-package-managers	-1s
e2e	-1s
e2e-snapshots	-1s
Browser Compatibility Tests	-1s
	11m 40s

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