Fixes #23281. Part of #20613.
We were emitting the `online` event in the constructor, so the caller
could never receive it (since there was no time for them to add a
listener). Instead, emit the event where it's intended – after the
worker is initialized.
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After this parcel no longer freezes, but still will fail due to other
bugs (which will be fixed in other PRs)
cb0c23a7f1