Add support new native majors

[tonidero]

This bumps PHC to 13.0.0 which includes breaking changes in the native SDKs:

• iOS v5: https://github.com/RevenueCat/purchases-ios/releases/tag/5.0.0
• Android v8: https://github.com/RevenueCat/purchases-android/releases/tag/8.0.0

[tonidero]

Want to test this better but this should be ready for review

[tonidero]

Ah yes thanks for the reminder! Will add that now

[fire-at-will]

The migration guide for Unity should be pretty similar to the react native one, just with Unity code samples instead of RN: https://github.com/RevenueCat/react-native-purchases/blob/main/migrations/v8-MIGRATION.md