If any logging is enabled (for instance with --prof), the calls into
Logger:ApiEntryCall become quite expensive.

Move the FLAG_log_api checks to the header to speed up these
high-frequency events.

Change-Id: Iba718c856cd57a890ad6b63bcf4b6836bfd5d3f0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3024156Reviewed-by: Patrick Thier <pthier@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75812}