We temporarily enable the StringForwardingTable for all ThinString
transitions behind --future to get coverage and performance numbers from
future bots.

Bug: v8:12007
Change-Id: Ia59bd6c40df2fd413867f6fc2aa7f69d099b5377
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3637799Reviewed-by: Shu-yu Guo <syg@chromium.org>
Commit-Queue: Patrick Thier <pthier@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80516}