This is a performance improvement; no change in functional
behavior is intended.
AdaptiveMap is an abstraction over a std::map or a std::vector:
after being initialized iteratively with a set of entries, it
can switch to dense vector-based storage if that would be more
efficient.
The motivation is that we expect most name sections, if they
are present at all, to give fairly complete information, so the
dense mode will likely be the typical case. However, it's easy
enough to support sparse mode as well, and parsing the name
section into a std::map at first is particularly convenient for
cases where we can't guess the expected number of entries, such
as for function locals.

Change-Id: Ia17f27576a3061eb05c912f7081411d6f38137e6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3726150Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81474}