This makes the code easier to read, and will also be helpful for the
extension to multiple indirect function tables.

R=clemensh@chromium.org

Bug: v8:9396
Change-Id: Idba143611e13f6b6cfc0e9d6c6f380ee3566db80
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1678476
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62390}