When trying to find a spot in the freelists for a tiniest object,
the tiny freelist was never searched.

This was fixed by modifying FreeList::Allocate in order to handle
that special case.
A test was added in cctest/heap/test-spaces.cc. It allocates a
Tiny object on a new page, then fills up the page, then frees the
first object, and finally tries to allocate a Tiniest
object. Before, this Tiniest object would go on a different page;
now it goes on the same one (which is what the test checks for).

Bug: v8:9329
Change-Id: Ia810726d1bfe1dae4ef2055a7f5b314b1514ee9c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1647162
Commit-Queue: Darius Mercadier <dmercadier@google.com>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62055}