next method
void
next()
Moves focus to the next focusable widget.
If a trap is active, only navigates within the trapped subtree.
Implementation
void next() {
final candidates = _getVisibleCandidates();
if (candidates.isEmpty) return;
final index = _focusedId == null ? -1 : candidates.indexOf(_focusedId!);
final nextIndex = (index + 1) % candidates.length;
requestFocus(candidates[nextIndex]);
}