stress_flush_bytecode controls stress flushing of both bytecode and
baseline code. So rename the flag to better reflect its functionality

Bug: v8:11947
Change-Id: Ie6c124a476c3a7c6eabd1d75de030ee15fe78e32
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3062567
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76043}