This fixes local names that are the string representation of a valid
element index.
Even though both the Liftoff and the interpreter-based test are changed,
only the latter needs to be fixed right now since Liftoff does not use
the names currently. Modifying the test just ensures that we implement
this correctly once we use the name.

R=jkummerow@chromium.org

Bug: v8:10019
Change-Id: Ib7f7d6e244a344a85ab540b6c2c67f98b1f3078e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1998079
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65751}