test: split heap snapshot limit tests

test/parallel/test-heapsnapshot-near-heap-limit.js is timing out in CI
on low-memory and slow-CPU devices. Split off the worker test to its own
test file to allow the test to finish in time.

Refs: https://github.com/nodejs/node/issues/36961
PR-URL: https://github.com/nodejs/node/pull/37189


Reviewed-By: Ash Cripps <acripps@redhat.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>