forked from loafle/openapi-generator-original
* [dart-dio] Enable strong-mode and strict types This will make it easier to eventually transition to NNBD. Also fix some formatting things. * [dart-dio] Add implicit-casts: false to analysis options * [dart-dio] Add dartanalyzer to integration tests * raise minimum Dart version to 2.6 (to support spread collection) * add header to all files for language version * fix some missing imports that can be fixed (some remain due to missing inheritance support)