It's not always easy to spot what exact configuration of V8 is run
within embedders. With --print-flag-values we can easily compare
different configurations.

Drive-by-fix:
- Use new FlagValue and FlagName helpers for printing
- Remove unused FlagList::argv helper

Change-Id: Ic8a25479d7b1e72f714b22ae7d2e56e06e810556
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3197713Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77189}