Currently, GetConsName incorrectly includes the null terminator as part
of the length used in the string's hash. Exclude this to be consistent
with GetCopy, GetName, etc. and permit coalescing.

Bug: v8:0
Change-Id: I1e8a4eb7055637f3ed178014725b44e84d7788b6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2578192Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Andrew Comminos <acomminos@fb.com>
Cr-Commit-Position: refs/heads/master@{#71667}