LocalHeap only uses LABs for allocation with size below
kMaxLabObjectSize. Larger allocations used a path that was unaware of
alignment restrictions.

Bring implementations of LocalHeap and regular PagedSpace closer
together by assuming the caller of their free list allocations takes
care of size and alignment adjustments.

Drive-by: Use unaligned allocations when possible which avoids a call
into PreceedWithFiller(size) which would only bail out late for
0-sized fillers.

Bug: chromium:1338687
Change-Id: I0f52c54359326a249b2ebe95bb73184ad95194f0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3721817Reviewed-by: Nikolaos Papaspyrou <nikolaos@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81338}