### Changes:
- `InternalAPI` is now `Sendable` to deal with new compilation error
- `PaywallEventStoreType` is now `Sendable`
- Extracted `SK2BeginRefundRequestHelperType` to make
`SK2BeginRefundRequestHelper` `Sendable`
- Updated `MockSK2BeginRefundRequestHelper` to be thread-safe and
`Sendable`
- Fixed compilation error in `DebugContentViews`
- Fixed compilation error in `DebugViewModel`
- Fixed compilation error in `StoreMessagesHelper`
Fixes https://github.com/RevenueCat/purchases-capacitor/issues/100 and
https://app.circleci.com/pipelines/github/RevenueCat/purchases-ios/14093/workflows/b3f8d001-6f39-40db-a5c5-00fc37d0211e/jobs/105838
```
Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0 ??? 0x0 ???
1 libswiftCore.dylib 0x18f9b8cf8 swift_getSingletonMetadata + 956
2 RevenueCat 0x107f42de4 type metadata accessor for DebugViewModel + 64
3 libobjc.A.dylib 0x18017d938 realizeClassMaybeSwiftMaybeRelock(objc_class*, mutex_tt<false>&, bool) + 116
4 libobjc.A.dylib 0x180184eb0 realizeAllClasses() + 168
5 libobjc.A.dylib 0x180187b3c objc_copyClassList + 36
6 XCTestCore 0x10532fcb0 +[XCTestCase(RuntimeUtilities) _allSubclasses] + 36
7 XCTestCore 0x10532fdb8 +[XCTestCase(RuntimeUtilities) allSubclasses] + 16
```
Both `XCTest` (to load tests at runtime) and `Capacitor` use
`objc_getClassList`. That's broken before iOS 16 and will try to load
the metadata for `DebugViewModel` even though it's not `@available`.
A similar issue has been reported before:
https://openradar.appspot.com/radar?id=4970535809187840 /
https://github.com/apple/swift/issues/58099
This adds a layer of indirection so loading `DebugViewModel` at runtime
doesn't require the metadata for `NavigationPath`.
### Context:
`#if os(iOS)` no longer evaluates to `true` when compiling for
`visionOS`
Which means we need `|| os(xrOS)`.
But to support older Xcode we need `#if swift(>=5.9) && os(xrOS)`.
But, fun fact, short-circuiting doesn’t work in `Xcode 13`.
And we still need that to run iOS <15 tests (`FB12223404` /
`FB12805891`)
💩
This works around that by defining our own `VISION_OS` flag.
### Changes:
- Added `VISION_OS` compile time flag to determine SDK
- Replaced `#if os(xrOS)` with `#if VISION_OS`
- Added flag to `Package.swift` (thanks @neonichu for helping with this)
NachoSoto