- Added `Offering.paywall`
- Decoding `PaywallData` in `OfferingsResponse`, using
`IgnoreDecodeErrors` (this will be better after #2778)
- New `PaywallData` `struct`
- Added new APIs to testers
- Testing paywall deserialization from `Offerings`
- Testing paywall deserialization separately to check edge cases

…#2781)

This adds a new `TemplateViewType` that different templates can conform
to.
`PaywallView` now takes `PaywallData` and renders the paywall depending
on its template.

### Other changes:
- Added `subtitle` and `offerDetails` to `LocalizedConfiguration`
- Improved sample paywall to include these with test variables
- Updated snapshot test to display the current progress
- Added initial implementation of `VariableHandler` with tests

![image](https://github.com/RevenueCat/purchases-ios/assets/685609/2e009460-5faf-42af-8dd0-8ff416e51335)

This allows configuring which package(s) will be displayed in each
paywall.

- Added `PaywallData.assetBaseURL` and
`PaywallData.Configuration.headerImageName`
- Changed template to fetch image from network
- Updated snapshot testing to support asynchronous checking, necessary
for `AsyncImageView`
- Added support for overriding images for snapshot tests
- Extracted `DebugErrorView`

Follow up to #2796.
This also makes `PaywallData.Configuration`'s intro strings optional.

### Other changes:
- Injected `TrialOrIntroEligibilityChecker`
- Created mock `TrialOrIntroEligibilityChecker` for previews
- Handling state and transitions for loading eligibility
- Snapshot tests for the different new cases
- Improved `SnapshotTesting` delay management
- Expanded `DebugErrorView` to customize release behavior

Had to join in the fun!

This PR updates the regex logic for variables to use RegexBuilder.

Some missing tests for the logic added in #2798.
I've also moved this function to be fined in `PaywallData` instead of
the `TemplateViewType` protocol, which makes more sense.

This adds a new `PurchaseHandler` type, which can be instantiated with
`Purchases` or with a mock implementation for previews. That gets
injected, and templates can now purchase and dismiss themselves.

I've improved the `SimpleApp` setup to better work with the lifetime of
purchases. Now it only displays the paywall if the user doesn't have an
entitlement.

I've also added some basic error handling to the new `AsyncButton`:
![Simulator Screenshot - iPhone 14 Pro - 2023-07-13 at 15 32
06](https://github.com/RevenueCat/purchases-ios/assets/685609/e8c2e6e3-f1e0-411f-9ca2-8a3cc3823a42)

These now match how the frontend is configuring them.

In the future we'll be able to polish support for those platforms.

This improves the layout of the template, and adds a scroll view that
optionally scrolls if the content is too large.
This can serve as a the basis for future templates.

![iOS16-testAccessibility3
1](https://github.com/RevenueCat/purchases-ios/assets/685609/40cb6929-d7f0-49d4-a9c5-7fdea9747db9)

…ewConfiguration` (#2830)

### Changes:
- Created `TemplateViewConfiguration` to encapsulate all processed
configuration for a paywall
- Created `TemplateViewConfiguration.PackageSetting` and
`TemplateViewConfiguration.PackageConfiguration` to represent paywalls
that support 1 or N packages
- Taken all common logic out of `Example1Template`
- Added new `PaywallViewMode` for upcoming "ramps" views

…#2832)

Changed `PaywallData.Configuration.headerImageName` to `imageNames`.
This more flexible definition allows future templates to display a
carrousel of images instead of a single image.

Depends on #2831.

This adds 2 new modes: `.square` and `.banner`:

![iOS16-testSquarePaywall
1](https://github.com/RevenueCat/purchases-ios/assets/685609/5d1a0a52-e02b-4877-90ac-fdeb2dcea058)
![iOS16-testBannerPaywall
1](https://github.com/RevenueCat/purchases-ios/assets/685609/a9f208d8-f920-4abd-a914-1dd86e940b1a)

-------

I've updated `Example1Template` to support both as an example, and added
that as snapshot tests.

This also adds a new constructor to `PaywallView` that doesn't require
passing an `Offering` or `PaywallData`, it automatically loads that from
`Purchases.shared`. With that, embedding these mini-paywalls is trivial:

```swift
struct MyApp: View {
  var body: some View {
    MyOtherViews()
    if !customerInfo.hasPro {
      PaywallView(mode: .card)
    }
  }
}
```

I've added these as examples to the testing app:

![simulator_screenshot_84270E1A-F7C6-4C5D-8773-F4F2E646CB0F](https://github.com/RevenueCat/purchases-ios/assets/685609/e368cab3-55af-4a87-88aa-b678deb5d2e5)

Small refactor, starting to take views out of `Example1Template` so
they're usable by other templates. This also removes some of the
duplicate code.