Change base::Optional to an alias of absl::optional. Eventually we
should remove it entirely.

Bug: v8:11006
Change-Id: I687d44cc7e7cd0a49a84bcc207231eb6808eef2d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2476318
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76913}