Detect changes to PBXBuildFile during build up-to-date checking

[lacasseio]

As a user building Xcode targets using Gradle, I want the Gradle tasks representing the Xcode targets to be out-of-date when its build file changes during an incremental build so I can have accurate feedback.

Acceptance Criteria

• [x] Any changes to settings, e.g. add new items, remove existing items. Ordering should have no effect.
• Gradle should check the content of file reference according to the build phase using the PBXBuildFile model.
• [ ] Using productRef (Swift PM) causes the task to always be out-of-date