Override to control the layout constraints given to each child.
By default, the children will receive the given constraints, which are the constraints used to size the container. The children need not respect the given constraints, but they are required to respect the returned constraints. For example, the incoming constraints might require the container to have a width of exactly 100.0 and a height of exactly 100.0, but this function might give the children looser constraints that let them be larger or smaller than 100.0 by 100.0.
If this function depends on information other than the given constraints, override shouldRelayout to indicate when when the container should relayout.
BoxConstraints getConstraintsForChild(int i, BoxConstraints constraints) => constraints;