method to put provided views into a vertical stack view.
• method to put provided buttons into a vertical stack view.
All these would allow me to update reg flow screens to look the same without specifying layout metrics multiple times.
• add "large primary", "large secondary", "medium secondary" SwiftUI button styles and use them.
• tweak subtitle font to match specs.
• use liquid glass button on iOS 26.
The old UIButton API is still functional as long as we don't use
UIButton.Configuration, so we can safely ignore these warnings until we're
ready to adopt the configuration API across the codebase.
