[8.2.x] fix(service-worker): ensure initialization before handling messages

[gkalpak]

This is a backport of #32525 to the 8.2.x branch.

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[mary-poppins]

You can preview 9d58db8 at https://pr33744-9d58db8.ngbuilds.io/.

[gkalpak]

merge-assistance: This needs to be merged into 8.2.x.
merge-assistance: This commit is already part of the master, so the author is OK with their commit being contributed to this project 😁

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[kara]

Closed in 2840670

[Splaktar]

@googlebot I consent.

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