[sparkplug][cleanup] Add helper to en-/decode VLQ.

VLQ encoding was implemented in TranslationArray and Sparkplug PC <->
bytecode mapping.
This CL introduces new VLQ helper methods used in both.

Bug: v8:11429
Change-Id: I89d9777eab4ad28f08e5957421b63df07e37f9cc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2704674


Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Patrick Thier <pthier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73054}