This is a reland of 1186fc50

This reland fixes NewSpaceAllocationTopAddress() and
NewSpaceAllocationLimitAddress() by returning nullptr if no new space
is available. This is okay since those are never used later on.

We can't make this a build-time flag because we may only want to disable
the new space for the shared heap.

Original change's description:
> [heap] Disable the young generation in shared heaps
>
> A shared heap will not have a young generation in the beginning.
>
> Bug: v8:11708
> Change-Id: I947ddb91a23a72a8cee3aa3e554723dda8146011
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2891569
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#74697}

Bug: v8:11708
Change-Id: I254b919f7076ce624d15c924e63cbde5eb4df749
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2912731Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74735}