Xcconfig file handling fix

[tothszabi]

Checklist

• I've read and followed the Contribution Guidelines
• step.yml and README.md is updated with the changes (if needed)

Version

Requires a MINOR version update

Context

The step was not handling the case when the info plist path is defined in an xcconfig file.

The new logic is that if the mandatory plist path is not in the project settings then it will use xcodebuild to resolve the xconfig files. And it uses xcodebuild because the xconfig files could import other xcconfig file so parsing them manually is not that simple.