- Present paywall only on save/connect because PurchaseRequiredButton
instances were presenting paywalls with partial requirements
- Retain PurchaseRequiredButton just to flag paid features visually, but
do nothing on tap
- Suggest paywall products via IAPManager and required features, rather
than from views
- Handle .sharing/.appleTV requirements in ProfileCoordinator, rather
than in StorageSection
- Discontinue platform purchases, but treat as full if iOS + macOS
There was duplication and a ugly `#if os(macOS)` with some footers
explicitly rendered on macOS with .themeFooter() (now .themeSubtitle()).
Move this logic to the .themeSection() modifiers by adding a
`forcesFooter` parameter. When true, a fake footer is added on macOS as
the last row of a section.