Currently we sometimes refer to baseline code or the baseline compiler
by its codename (Sparkplug). The codename is fun, but we should be
consistent and call things by one name or the other. Following the
pattern of Ignition stuff being called "interpreter", we call Sparkplug
"baseline", and leave the codename only in flags and variants.

Bug: v8:11420
Change-Id: I432e5629518be7c7ad38b6acff024c91d4cfd6d3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2692186
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72696}