worker: fix crash when SharedArrayBuffer outlives creating thread

Keep a reference to the `ArrayBuffer::Allocator` alive for at least
as long as a `SharedArrayBuffer` allocated by it lives.

Refs: https://github.com/nodejs/node/pull/28788
Fixes: https://github.com/nodejs/node/issues/28777
Fixes: https://github.com/nodejs/node/issues/28773

PR-URL: https://github.com/nodejs/node/pull/29190


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>