This adds an output operator for {RegisterBitVector}, mostly for getting
better DCHECK error messages.

R=thibaudm@chromium.org

Bug: v8:12330
Change-Id: I98f822f94a3b6a240c8ead7ea4de4049abe9998e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3372909Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78512}