[iOS][PT] Fix drop animation

This CL checks that there is no local drag action before ending the drag
session.

Fixed: 1425119
Change-Id: I17655bf66128a5714f3ac573488470e52ce1c03e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4346832


Reviewed-by: Louis Romero <lpromero@google.com>
Commit-Queue: Ewann Pellé <ewannpv@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1118650}