Whether to collapse the selection when it would otherwise reverse order.
For example, consider when forward is true and the extent is before the base. If collapseAtReversal is true, then this will cause the selection to collapse at the base. If it's false, then the extent will be placed at the linebreak, reversing the order of base and offset.
Cannot be true when collapseSelection is true.
final bool collapseAtReversal;