Re-open from https://github.com/flutter/flutter/pull/116551

This PR added optional labelText (which will be  rendered side by side with Checkbox in the future, and thus is also announced by default by screen readers), and semanticLabel(which will be announced by screen reader if provided, overrides labelText, in order to do that we might want to wrap the Text widget inside ExcludeSemantics in the future).

Issues fixed:
[b/239564167]