resetCell method
Implementation
void resetCell(int index) {
final offset = index * _cellSize;
_data[offset + _cellForeground] = 0;
_data[offset + _cellBackground] = 0;
_data[offset + _cellAttributes] = 0;
_data[offset + _cellContent] = 0;
_underlineColors.remove(index);
_combiningCharacters.remove(index);
}