JSON schema - tailing double quotes for maximum (#6452)

JSON schema - tailing double quotes for maximum (#6452)

* Fix C/C++ Create<Type>Direct with sorted vectors

If a struct has a key the vector has to be sorted. To sort the vector
you can't use "const".

* Changes due to code review

* Improve code readability

* Add generate of JSON schema to string to lib

* option indent_step is supported

* Remove unused variables

* Fix break in test

* Fix style to be consistent with rest of the code

* Fix  double quotes for (u)int8 in json schema

* Fix reference file for JSON schema test

* Fix reference file for JSON schema test