This CL extracts a function which reads from a buffer and additionally
increments an offset for the next read.

R=clemensb@chromium.org

Bug: v8:10281, v8:10155
Change-Id: Id8d79130cde17053d701d2508e40cba993471e55
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2101001
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66707}