Introduce SemanticProperties.IsCheckable

[rachelkang]

Consider formalizing Semantic IsCheckable in a new property SemanticProperties.IsCheckable

The work has been started with RadioButton on iOS - we created a SemanticSwitchContentView which overrides accessibility traits of a Contentview and sets it to a Switch's accessibility traits (to ultimately make RadioButton behave as a switch on iOS)

#10832

Formalizing this as a separate property would not only help clean up the code but also allow for it to be applied to other controls more efficiently

cc @PureWeen

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.