[iOS] Fix Add to Group in TabGrid selection

If shareable and non-sharable tabs are selected, they should all be
movable to new or existing tab group using the selection mode in the
TabGrid.

Fixed: 331745630, 328425613
Change-Id: Ia9277351e4a3530b67f0fe95facf14876fa5ec05
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5401801


Auto-Submit: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Louis Romero <lpromero@google.com>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280134}