Tab constructor
Creates a Material Design TabBar tab.
At least one of text, icon, and child must be non-null. The text
and child arguments must not be used at the same time. The
iconMargin is only useful when icon and either one of text or
child is non-null.
Implementation
const Tab({super.key, this.text, this.icon, this.iconMargin, this.height, this.child})
: assert(text != null || child != null || icon != null),
assert(text == null || child == null);