GoldenFileComparator constructor Null safety

1. Flutter
2. flutter_test
3. GoldenFileComparator
4. GoldenFileComparator constructor

GoldenFileComparator class

1. Constructors
2. GoldenFileComparator
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. compare
8. getTestUri
9. noSuchMethod
10. toString
11. update
12. Operators
13. operator ==
14. Static methods
15. compareLists