LDKind constructor Null safety

1. launchdarkly_flutter_client_sdk
2. launchdarkly_flutter_client_sdk
3. LDKind
4. LDKind const constructor

LDKind enum

1. Constructors
2. LDKind
3. Values
4. OFF
5. FALLTHROUGH
6. TARGET_MATCH
7. RULE_MATCH
8. PREREQUISITE_FAILED
9. ERROR
10. UNKNOWN
11. Properties
12. hashCode
13. index
14. runtimeType
15. Methods
16. noSuchMethod
17. toString
18. Operators
19. operator ==
20. Constants
21. values