Assert macOS framework artifact contains xcprivacy manifest (flutter#155189)

Add tool test to validate a built macOS app contains the FlutterMacOS framework xcprivacy manifest.

Blocked on flutter/engine#55078 rolling in.

Author: jmagman

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

@@ -225,6 +225,7 @@ void main() {
       expect(outputFlutterFramework.childDirectory('Headers'), isNot(exists));
       expect(outputFlutterFramework.childLink('Modules'), isNot(exists));
       expect(outputFlutterFramework.childDirectory('Modules'), isNot(exists));
+      expect(outputFlutterFramework.childFile('PrivacyInfo.xcprivacy'), exists);
 
       // Build again without cleaning.
       final ProcessResult secondBuild = processManager.runSync(buildCommand, workingDirectory: workingDirectory);