This is a follow-up to #162093.

The following cupertino widgets should use the SemanticsRole.radioGroup as automatically as possible:

• CupertinoSegmentedControl
• CupertinoSlidingSegmentedControl
• CupertinoRadio
• Note: RadioListTile is captured as part of [a11y] apply radioGroup role to material widgets #164584. RadioListTile.adaptive picks between CupertinoRadio and material Radio automatically.

It may not be possible for some widgets to automatically create a group. For example, a CupertinoRadio or RadioListTile alone does not form a group. However, when they are in a group, they should participate seamlessly.

Widgets that have a clear intent to form a group of radio widgets, should apply the radioGroup role automatically, such as CupertinoSegmentedControl and CupertinoSlidingSegmentedControl that contain groups of exclusive radios.

See also the material version of this issue: #164584