Ensure that the reorder preview and what gets submited uses the same solution.

Design doc: https://docs.google.com/document/d/1RsId9OFGgkcImkkmDwWZBBvITWnGlxKVqniE3cimkqY/edit#heading=h.xzptrog8pyxf

As can be seen in the diagram in b/256770363 on every reorder the
first call in the process is MODE_SHOW_REORDER_HINT so if we make
sure that only then a solution is calculated and we reuse that
solution in the rest of the calls in the same reorder then we would
have more consistency and the animation will always be the same and
the logic state.

Fix: 256770363
Bug: 188081026
Test: atest ReorderWidgets
Change-Id: I93a1d09f5b8cbfbc461043ee3fc41b1cab294fed