OOBE: Ensure ChromeVox hint content respects tablet mode

Bug: b/335793447
Change-Id: Id685b602f09389e57522e472c690fce118c26215
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5604908


Commit-Queue: Akihiro Ota <akihiroota@chromium.org>
Reviewed-by: Danila Kuzmin <dkuzmin@google.com>
Cr-Commit-Position: refs/heads/main@{#1312824}