In particular: MapForFixedTypedArray() and EmptyFixedTypedArrayForMap().

And make ReadOnlyRoots object independent of the Heap.

Bug: v8:8015
Change-Id: Ifd17294661fac21c8e7545145280c8a2dedfe8c3
Reviewed-on: https://chromium-review.googlesource.com/1243131Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56234}