[cleanup] Templatize AsAtomicWordX and AsAtomicPointer definitions

Bug: v8:8238
Change-Id: I7fa1538909bfaf368498ebcc1c59eed258e81a16
Reviewed-on: https://chromium-review.googlesource.com/c/1352272Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57877}