simple appbar transition to appbar with textField
example https://taljacobson.github.io/flutter_search_bar_transition/#/
based off NishantDesai1306/flutter_search_bar_transition
most of the properties are the same as with AppBar except for the addition of
/// callback for when closing
final VoidCallback onCancelSearch;
/// search Seach icon container overide
final Widget searchIconContainer;
/// text controller -- required
final TextEditingController searchController;
/// reveal color -- defaults to `theme.of(context).accentColor`
final Color revealColor;
/// duration for transition -- defaults to `Duration(milliseconds: 300)`
final Duration duration;