[iOS] Fix drag and drop in group

This CL fixes several bugs related to Drag and Drop in the grid:
- Dropping an external URL in the Tab Group View
- Dropping an existing tab in the Tab Group View
- Dropping an internal URL in the Tab Group View

Fixed: 345319580, 345709820, 345701796
Change-Id: I93a74d831faaebdee50e9858ac090bc71136b845
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5604504


Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Auto-Submit: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Ewann Pellé <ewannpv@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1312678}