Add flatc option to inhibit all warnings #6005 (#6301)
* 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
* Add option --no-warnings to inhibit all warnings
* Fix order of member initialization
* Add documentation for --no-warnings