Reorder widgets no longer overlaps when no space is available

In the previous refactor I got confused between findNearestVacantArea
and findNearestArea thinking the later did the former. So it ignored the occupied spaces and treat it as a solution.

Changed the names to prevent further confusion.

Fix: 258023561
Test: manual, need to add this case to ReorderWidgets
Change-Id: I04b262ecce168d5c93a9d66ef62d5b0e148e38b6