[IOS][OR] Relocate OnAfterPossibleChange to text controller

The goal is to remove the OmniboxEditModel, this CL and upcoming CLS
aim to move logic from the edit model to the controllers.

Bug: 426154586
Change-Id: I9013e90b6ba2c108b329f152f31a3827a96c7e15
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6668419
Reviewed-by: Christian Xu <christianxu@chromium.org>
Commit-Queue: Ameur Hosni <ameurhosni@google.com>
Auto-Submit: Ameur Hosni <ameurhosni@google.com>
Cr-Commit-Position: refs/heads/main@{#1478477}