direction property
Determine the SuggestionBox's direction.
If AxisDirection.down, the SuggestionBox will be below the TextField
and the _SuggestionsList will grow down.
If AxisDirection.up, the SuggestionBox will be above the TextField
and the _SuggestionsList will grow up.
AxisDirection.left and AxisDirection.right are not allowed.
Implementation
final AxisDirection direction;