[iOS] Temporarily disable scroll-to-top gesture when looking at a tab group

When the tab group contents were shown, the scroll-to-top (tapping on
the status bar) gesture was received by the underlying regular tab grid
view controller. This is because On iPhone, the scroll-to-top gesture
has no effect if there’s more than one scroll view onscreen that has
`scrollsToTop` set to true.

This CL disables scroll-to-top for any grid that support tab groups
when the tab group is shown and re-enables it when it is dismissed.

Video:https://drive.google.com/file/d/1Tf8GD5DnpjALFJyOEKtuE643qdcR9l60

Fixed: 344842090
Change-Id: Ida7dcf405b72724ff5dd01bd03345135343fd409
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5612416


Commit-Queue: Radu Nitescu <radunitescu@google.com>
Reviewed-by: Aliona Dangla <alionadangla@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1312840}