Assert iOS framework artifact contains xcprivacy manifest (#155187)

Add tool test to validate a built iOS app contains the Flutter framework xcprivacy manifest.

Follow up to https://github.com/flutter/engine/pull/48951.

packages/flutter_tools/test/host_cross_arch.shard/ios_content_validation_test.dart

@@ -159,6 +159,8 @@ void main() {
           // Plugin is a dynamic xor static framework.
           expect(helloDynamic != helloStatic, isTrue);
 
+          expect(outputFlutterFramework.childFile('PrivacyInfo.xcprivacy'), exists);
+
           expect(outputAppFrameworkBinary, exists);
           expect(outputAppFramework.childFile('Info.plist'), exists);