This is a reland of 8d3c8093 to make
UBsan happy: memcopy (and therefore MemCopy) seems to expect a non-null
src even when the given size is 0, so avoid calling it in that case.

Original change's description:
> [factory] Make NewByteArray return canonical empty byte array
>
> ... for length = 0, analogously to what e.g. NewFixedArray does.
>
> Simplify some call sites that had special handling for this case
> (there are others that didn't).
>
> Change-Id: Ib3de5506300e967aca072fad53df7ab04ef68839
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3009225
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Commit-Queue: Georg Neis <neis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#75629}

Change-Id: Ib8dc471d63a4b11b846e9d436555a3615902b66f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3014456Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75642}