Fix Split animations after single-root

The animations were modifying the single-root surface, but that
surface isn't expected to be modified. This would cause the
single-root to be alpha=0 permanently.

This also disables pip-entry when drag-divider-to-dismiss since
that isn't supposed to happen.

Bug: 226673164
Test: split with auto-pipable, drag-divider to dismiss pipable,
      go to recents, enter-split again with same apps.
Change-Id: Ia1f304efd1dbf4434e628d2b7723a2afaae43a34