handleSelectAll function
Implementation
bool handleSelectAll(FluentDocument document) {
final root = document.content;
final cursor = document.cursor;
if (root.nodes.isEmpty) return false;
final stops = document.caretStops;
if (stops.isEmpty) return false;
final firstStop = stops.first;
final lastStop = stops.last;
cursor.moveTo(firstStop.fragmentId, firstStop.offset);
cursor.focusTo(lastStop.fragmentId, lastStop.offset);
syncSelectionManager(document);
document.cursorOnlyUpdate();
return true;
}