Members of DgsConstants don’t have a Reproducible Order

[jGleitz]

The members of the generated DgsConstants class can change order across builds. This creates an issue with build caching: Since the code generation is an input to the compilation, which is, in turn, a dependency for other tasks, changing the outputs of the code generation has a trickle-down effect and causes other dependent tasks to also need to be re-built.

Expected behaviour: Given the same input, the code generators always generate the same code.