Fix memory leak in _SelectableTextState (#135049)

packages/flutter/lib/src/material/selectable_text.dart

@@ -536,6 +536,7 @@ class _SelectableTextState extends State<SelectableText> implements TextSelectio
     super.didUpdateWidget(oldWidget);
     if (widget.data != oldWidget.data || widget.textSpan != oldWidget.textSpan) {
       _controller.removeListener(_onControllerChanged);
+      _controller.dispose();
       _controller = _TextSpanEditingController(
           textSpan: widget.textSpan ?? TextSpan(text: widget.data),
       );