This is a reland of b354e344

This CL adds 3 fixes:

* Unprotect code object before creating filler
* Allows AllocationObserver::Step to add more AllocationObservers
* Update limit in NewSpace::UpdateLinearAllocationArea

Original change's description:
> [heap] Refactor allocation observer in AllocationCounter
>
> 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}

Bug: v8:10315
Change-Id: I89ab4d5069a234a293471f613dab16b47d8fff89
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2332805Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69216}