[ios] Collect all functions under the same unnamed namespace

This CL is just a clean up to put all functions under the same unnamed
namespace. No logic changes.

Change-Id: Ic13d2131d01b96fc0b45e47f5869009306dfef15
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6237074
Commit-Queue: Asami Doi <asamidoi@chromium.org>
Auto-Submit: Asami Doi <asamidoi@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1416718}