Optional delegate for building the text selection handles.
Historically, this field also controlled the toolbar. This is now handled by contextMenuBuilder instead. However, for backwards compatibility, when selectionControls is set to an object that does not mix in TextSelectionHandleControls, contextMenuBuilder is ignored and the TextSelectionControls.buildToolbar method is used instead.
- CupertinoTextField, which wraps an EditableText and which shows the selection toolbar upon user events that are appropriate on the iOS platform.
- TextField, a Material Design themed wrapper of EditableText, which shows the selection toolbar upon appropriate user events based on the user's platform set in ThemeData.platform.
final TextSelectionControls? selectionControls;