* [dart-dio] Adds support for generating inline enums
Previously these were generated as strings if declared inline in the spec.
* Adds more detailed comment about inline enums
* [dart-dio+time_machine] Add missing import, serializer
* [dart-dio] Remove bad import from `http` package
* [dart-dio] Use raw strings for those that contain variable name.
This should eliminate potential issue with variables like `$ref`.
* [dart-dio] Use `_path` instead of `path` to avoid potential conflict with op params.
See 1bec0b47b1/Kubernetes.json, there are a few with `{path}` param.
* [dart-dio+time_machine] Use `OffsetXxx` classes for date time values
- due to the addition of the timemachine library, models were importing ‘DateTime’ when using the core library, which is not a valid import.
- the parameterToString function was copied from the dart2 generator and had some errors when some enums were classes.
