... /objects/concurrent-string-unittest.

- Add AsciiToTwoByteString to convert ascii string to
two byte string.

Bug: v8:12781
Change-Id: Icc2f745846fa10ec940085eab0ef022d7c277e0a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3600552Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: 王澳 <wangao.james@bytedance.com>
Cr-Commit-Position: refs/heads/main@{#80101}