Revert "[iOS] Remove scrolling broadcasting"

This reverts commit 3fd499229e357b96767be9c905b8cdf8ec9d754e.

Reason for revert: Likely causing FullscreenBrowserAgentTests Failures https://ci.chromium.org/ui/p/chrome/builders/ci/iphone-simulator/44966/overview

Original change's description:
> [iOS] Remove scrolling broadcasting
>
> The current implementation of the broadcaster implies a lot of
> unnecessary layers. It also listen to value change instead of using
> existing API. This CL removes the scrolling event in order to simplify
> the current code and just listen to the classical API.
>
> Change-Id: I5af7d77636be2decb1bbcf730d3af5ba95c5bf73
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4784148
> Commit-Queue: Aliona Dangla <alionadangla@chromium.org>
> Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
> Reviewed-by: Gauthier Ambard <gambard@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1185179}

Change-Id: Id2c95fde37e0f42bb288a3c8505f69229cd0caed
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4794571
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Cheick Cisse <cheickcisse@google.com>
Cr-Commit-Position: refs/heads/main@{#1185304}