Sketch of VoiceOver SwiftUI previews

[DavidBrunow]

This pull request is a sketch of what VoiceOver SwiftUI previews could look like.

Here are some decisions I made in this implementation:

• Created a modifier that could be added on top of an existing preview so multiple previews were not needed. This means that a button must be pressed, or a binding must be set to true, to see the VoiceOver preview
• Used the existing AccessibilitySnapshotView, including the snapshot of the content, rather than rendering the bounding boxes on top of the existing view
• Placed the legend below the view that has been snapshotted

Here is a screen recording of the preview in action:

Screen.Recording.2024-03-10.at.20.14.43.mov

[DavidBrunow]

I had to create a new podspec to be able to import AccessibilitySnapshotCore into the code files with the previews.