Expose JsonReporter for extension

[youssef-t]

Hello,

Currently, the JsonReporter can be used as it is provided by the package. But, it is complicated to extend its functionnality or change its behavior because JsonReporter depends on classes that are not visible outside the package: https://github.com/jonsamwell/dart_gherkin/tree/master/lib/src/reporters/json

For the package users, the only way to override the behavior of JsonReporter is to "copy paste" all its dependencies.

Will it be possible to expose publicly the folders containing the JsonReporter dependencies ?

Thank you