insertAbove method
Inserts an entry above below in the overlay stack.
Implementation
void insertAbove(OverlayEntry entry, {required OverlayEntry below}) {
final index = _entries.indexOf(below);
setState(() {
entry._overlayState = this;
if (index >= 0) {
_entries.insert(index + 1, entry);
} else {
_entries.add(entry);
}
});
}