setSelection method
Set selection on the terminal from base to extent. This method takes
the ownership of base and extent and will dispose them when the
selection is cleared or changed.
Implementation
void setSelection(CellAnchor base, CellAnchor extent, {SelectionMode? mode}) {
_selectionBase?.dispose();
_selectionBase = base;
_selectionExtent?.dispose();
_selectionExtent = extent;
if (mode != null) {
_selectionMode = mode;
}
notifyListeners();
}