Add support for private previews

[sergio-sastre]

It seems I was wrong and Classgraph could also scan private @previews

I'd like to extend the app to add support for private views accordingly. The default would not include private previews, but can be enabled with .includePrivatePreviews()

like this

AndroidComposablePreviewScanner()
    .scanPackageTrees("your.package", "your.package2")
    .includePrivatePreviews()
    .getPreviews()

[sergio-sastre]

Resolved in 0.1.3