Add SwiftUI examples in guidelines

Updated sections are:
- Element trait
- Text alternatives
- Date, time and numbers
- Trigger a vocalization
- Notify a content change
- Change the vocalization language
- Hide elements
- Grouping elements
- Reading order
- Custom content provider
- Focus on element
- Modify the focus area of VoiceOver
- Modal view (nothing found yet in SwiftUI API nor comments to add)
- Text size (f34beff)

Fixed typos=
- Bad variable name

Co-authored-by: Pierre-Yves Ayoul <[email protected]>
Co-authored-by: Pierre-Yves Lapersonne <[email protected]>
Reviewed-by: Pierre-Yves Ayoul <[email protected]>
Reviewed-by: Pierre-Yves Lapersonne <[email protected]>