Animation when extending textField

[SimonLab]

When the TextField obtains focus (see #308), the height of the widget is maxed out to take as much screen as possible. However this transition is a bit abrupt and I'm wondering if it's possible to have a smoother transition.

I'm going to research if it's possible to apply any nice effects to create this transition. Some more documentation to read: https://docs.flutter.dev/development/ui/widgets/animation