... for more consistent naming and less boilerplate.

Getters now use the `lower_case_flag()` style. Setters now use the
`set_lower_case_flag()` style.

Bug: v8:8888
Change-Id: I5af35b13a013bf303c4ca8d86f926754af28bfce
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2237139
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68293}