coral: Add toast when clicking on the chip with max desks

Adds a toast when we click and we cannot add a desk anymore.

The crash is because we extract the group from the birch coral
provider which removes it. Then when we try to open the selection
view we try getting the group from the birch coral provider, but
it has already been removed.

There have been reports of double clicking while not at max desks
also crashing with the same stack trace, but I haven't been able
to repro yet.

Test: ash_unittests CoralControllerTest.ClickChipWithMaxDesks
Bug: 376549527
Change-Id: If03577abb3e21c512079cfd748f0151ea3b3d6bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5981370
Commit-Queue: Xiaodan Zhu <zxdan@chromium.org>
Auto-Submit: Sammie Quon <sammiequon@chromium.org>
Reviewed-by: Xiaodan Zhu <zxdan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1376572}