[iOS] Fix cloud slash icon in bookmark, readinglist and password

This patch adds kCloudSlashSymbolPointSize and CloudSlashTintColor()
to return the size and the color of a cloud slash icon.

Change-Id: I1f80e860040ec08142ff03865c1d333af159a15e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4359672
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Victor Vianna <victorvianna@google.com>
Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1121140}