Remove Icon.Content and replace it with ViewBuilder parameters

[PavelHolec]

This is another task to make call site being able to inject any @ViewBuilder and make our wrapper components more simple and flexible. Now it is updated only for Icons, but follow-up tasks will clean up "disclosure", "buttons" and similar component properties.

The @ViewBuilder Icon closure differs based on components - sometimes, the component does not make sense without an icon, in which case, the closure is not optional.

For some components in future that would contain a large amount of ViewBuilders, we may even extract optional disclosure and other subviews as modifiers, similar to toolbar() modifier.

Inspiration from SwiftUI components

In general, most, if not all, SwiftUI components and modifiers follow these principles:

• the first argument has no name, if it is the primary property of that component (Label("label", icon:) vs. frame(width:, height:))
• parameter list ends with:
  • action handlers, sorted from primary action (tap, select) to secondary action (onCancel)
  • @ViewBuilders, sorted from primary content to secondary content (icon)

Label

A title is the primary information (goes first), an icon is secondary. The component is correctly able to detect EmptyView to avoid empty space in the HStack (we are doing the same in components that use Icon, although without access to internals of viewbuilder layout, we cannot correctly detect if/else/foreach empty cases).

// Full customization 
init(@ViewBuilder title: () -> Title, @ViewBuilder icon: () -> Icon)
// Basic init
init(_ title: S, systemImage name: String) where S : StringProtocol

DisclosureGroup

The primary "content" goes as a first @ViewBuilder.

init(isExpanded: Binding<Bool>, @ViewBuilder content: @escaping () -> Content, @ViewBuilder label: () -> Label)

PayWithApplePayButton

Actions go first, then @ViewBuilders

init(_ label: PayWithApplePayButtonLabel = .plain, action: @escaping () -> Void, @ViewBuilder fallback: () -> Fallback)