[iOS] Reenable testInputAccessoryBarIsPresentAfterPickers on iPhone simulator

Reduced the number of calls to [GetFirstResponder() reloadInputViews] in didRegisterFormActivity, because this was firing every time we were switching between username and password fields, for instance. Also re-enabled testInputAccessoryBarIsPresentAfterPickers, which tests this case, on iPhone simulator, for now (will try reenabling on device also if this is successful).

Bug: 325597035
Change-Id: Ifdbe4eb82f484b6555babccb0799b48ee9fd5d26
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5380764
Reviewed-by: Tommy Martino <tmartino@chromium.org>
Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1277011}