WWDC2022-10127: setup previewVisualizer

Following along with video from here https://developer.apple.com/videos/play/wwdc2022/10127/?time=410

At 6:50 mark we set up setup previewVisualizer, but we're not actually shown the implementation of this type. I think it would be helpful as I am having a hard time showing white visualizing lines that appear when scanning.

WWDC2022-10127: setup previewVisualizer
 
 
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