[iOS][TabStrip] Only reconfigure items in the snapshot

This CL ensures only items from the data source snapshot can be reloaded
through `reconfigureItems`.

Bug: 333377248
Change-Id: I9f9264c10ebe48b16d4412929714a933a79c14dd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5435279


Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Quentin Pubert <qpubert@google.com>
Cr-Commit-Position: refs/heads/main@{#1283921}