Tidy up SwiftUI/Onboarding screens

[pixlwave]

This PR touches a lot of files, and is probably easier to review the commits in order. They do as follows:

• Drops all iOS 13/14 availability checks across the onboarding flow and templates.
• Simplifies the FontValues struct
• Fixes alignment and truncating of localised strings on the Use Case screen on small devices.
• Uses the readableFrame modifier and OnboardingIconImage in the places that were using standard view modifiers.

Note: The last step to follow on the Use Case screen will hopefully be adding a blur to the footer when there is content behind it in a similar style to a navigation/tab bar.

Use case screen top	Use case screen bottom

[github-actions]

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[Anderas]

Nice spring clean

[SBiOSoftWhare]

Thanks for this cleanup!