Fix RegExpIndicesArray by adding undefined to type definition #35310

Job	Run time
package-size	1m 30s
lint	1m 1s
typecheck	1m 10s
baselines	8m 55s
coverage	10m 17s
browser-integration	1m 43s
smoke	1m 3s
Test Node 24 on windows-latest	10m 7s
Test Node 24 on ubuntu-latest	8m 35s
format	28s
self-check	59s
misc	26s
Test Node 14 on ubuntu-latest	11m 12s
Test Node 14 on windows-latest	14m 23s
Test Node lts/* on ubuntu-latest with --no-bundle	10m 56s
knip	36s
required	3s
	1h 23m 24s

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