GetIterator on object o consists of two steps:
1) iter = load o[#Symbol.Iterator]
2) call iter

For null / undefined step (1) throws an exception, meaning
step (2) is never reached. Up to this change, turbofan
deopts if for either of the two steps there isn't enough
feedback, meaning that we have a deopt loop for null and
undefined.

Change-Id: Ie0eaf8e231a149313e10af9e95fd80bc77dc0beb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3890980Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Auto-Submit: Matthias Liedtke <mliedtke@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83159}