Detect changes to PBXHeadersBuildPhase during target build up-to-date checking

[lacasseio]

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Xcode targets using Gradle, I want the Gradle tasks representing the Xcode targets using PBXHeadersBuildPhase to be out-of-date when its build specification change during an incremental build so I can have accurate feedback.

### Sub-Stories
- [ ] https://github.com/nokeedev/gradle-native/issues/788

Acceptance Criteria

• [ ] ~~Changes to the build phase name don't cause the task to be out-of-date. The name of a build phase is only an organizational tool and does not impact the build itself.~~ (Cannot change this build phase name via IDE)
• [x] Any changes to files, e.g. adding new items or removing existing items. ~Ordering change should have no effect.~ (We decided against ignoring ordering)
• [x] Any change to the content of the files/directories represented by files.