Fix smallest width configuration calculation

For calculating the smallest width, we need to iterate through all possible
orientations, snap the task bounds to a valid snap target and then use the
smallest width across all orientations.

In addition to that, when flinging the divider handle to the bottom of the
screen, we need to pass in fullscreen task bounds to avoid that this new
logic applies so the maximizing app only receives one configuration change.

Change-Id: I37aa9a40938517dfaf26770eb41327d76aec7c62
Fixes: 28469673