Worklist uses a singly-linked list of segments to hold entries.
Segment size was based on a compile-time constant but already stored
in the segment itself.

Rework the segments to query `malloc_usable_size()` on allocation and
adjust the capacity properly. For PartitionAlloc, it turns out that
there's ~20% more capacity available for the 64-element segments.

This slows down actual allocation of the segments with the upside of
improving utilization and requiring 20% less segments.

Change-Id: Ib8595c3fb9fb75b02e4022f6c525bb59a2df7ab7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3826047
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82432}