Removed the Firebase-specific references `appName` and `appID` from `GACAppAttestArtifactStorage`. They have been moved up one layer into `GACAppAttestProvider`.
Publicly exposed the initWithApp:appCheckProvider: constructor in GACAppCheck for the non-Firebase-specific App Check SDK. Since an AppCheckProvider is explicitly specified when constructing this generic App Check SDK, the AppCheckProviderFactory protocol / pattern / functionality is no longer used.
Added a podspec for AppCheckInterop and added it as a dependency in the existing AppCheck podspec. This is a lightweight, protocol-only, dependency that non-Firebase SDKs can make use of.
- Renamed FIR-prefixed symbols to GAC in unit tests for the generic (non-Firebase-specific) App Check SDK.
- Removed SharedTestUtilities/AppCheck* directories from the unit_tests spec sources (imports already changed to AppCheck/Tests/Utils/AppCheck*).