[iOS] Add TabGroups to Tab Search

This CL makes sure that the Tab Search is working with TabGroups.
It is also removing the TabGroup section in the TabGrid, displaying the
groups in the same space as the tabs.

It updates the commands to open the Tab Grid:
- Removes the DCHECK making sure the Tab Grid is not opened, moving
  it to an early return
- Adds an enum to ensure the right mode is used
- Merge the two existing methods

https://screencast.googleplex.com/cast/NDkxNTQ2MTY0MzgyOTI0OHxhNWQ5NGMxNC1jYw

Bug: 1501837
Change-Id: Ie1f60f96ad06d7d5a6cc80d90e50522f869abf48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5401656


Reviewed-by: Louis Romero <lpromero@google.com>
Auto-Submit: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1279565}