[DEPS] Add abseil to deps

Add a dependency on the chromium abseil-cpp subdir mirror.

Bug: v8:11006
Change-Id: Icaad757269d27c65bc368ed539f84c5bb79ee62d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2464940


Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70786}