Change SlotSet representation to a variable-sized array of pointers to
buckets. The length of the array/number of buckets depends on the size
of the page.
Before this change the SlotSet always stored a fixed number of
buckets. Large pages needed a SlotSet-Array to cover the whole object.

Now both regular and large pages both use a single SlotSet object,
which contains all bucket pointers.

Change-Id: I2d8d62fad54b58409cd39ae7a52c64497ee7c261
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1876811Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64635}