Moves accounting of allocation observers into the AllocationCounter
class. This CL removes top_on_previous_step_ for counters that are
increased regularly in the slow path of the allocation functions.

AdvanceAllocationObservers() informs the AllocationCounter about
allocated bytes, InvokeAllocationObservers() needs to be invoked when
an allocation step is reached. NextBytes() returns the number of bytes
until the next AllocationObserver::Step needs to run.

Bug: v8:10315
Change-Id: I8b6eb8719ab032d44ee0614d2a0f2645bfce9df6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2320650
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69170}