[ios] Fix 0 tabs created by "New Tab Group" in the selection mode

Before this CL, -didChangeWebStateList: in BaseGridMediator is called
multiple times when a new group is created from selected items.
1. -didChangeWebStateList: with kGroupCreate is called
2. -didChangeWebStateList: with kStatusOnly or kMove is called
3. -didChangeWebStateList: with kGroupDelete is called if a group is
selected
In Step 3, a deleted group is removed from `_selectedEditingItems` but the count of selected tabs doesn't reflect correctly because the
deleted group has 0 tabs. It causes the issue that an empty group with
0 tabs keeps being selected.

This CL fixes the issue by considering the creation of a group in
a batch operation. This makes -didChangeWebStateList: return early
and clears all selected items in -webStateListBatchOperationEnded:.

screen recording: https://drive.google.com/file/d/1LeMlvwpunrixfCd-64SWVnj6tC37dZ9q/view?usp=sharing

Bug: 380234933
Change-Id: I1cbd6bcc99ac22c716ad8bcfb6a8dacc2f4b6efa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6049199
Reviewed-by: Louis Romero <lpromero@google.com>
Commit-Queue: Asami Doi <asamidoi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1388783}