Convert constructor Null safety

1. irte_engine
2. convert
3. Convert
4. Convert constructor

Convert class

1. Constructors
2. Convert
3. Properties
4. hashCode
5. runtimeType
6. Methods
7. noSuchMethod
8. toString
9. Operators
10. operator ==
11. Static properties
12. kmToM
13. milesToM
14. mpsToKmh
15. mpsToMih