☂️ Support Kotlin Features

[HosseinYousefi]

Now that we're parsing Kotlin's metadata, we could start adding more and more specific support for Kotlin features. This is an umbrella issue for all these features. Feel free to add more.

• Kotlin inline classes #1164
• Generate Dart extensions from Kotlin extension methods #670
• Generate a corresponding top-level function from Kotlin's top-level functions #608
• Dealing with Tasks in jnigen #609
• Generate null-aware types from Kotlin #1165
• Kotlin operator overloading #1166
• Write Kotlin Docs in the generated code #598
• Use Kotlin signature in the doc comments of Kotlin methods #1236
• Generate Kotlin closures as Dart closures #1386

[HosseinYousefi]

Most used Kotlin features are done for the common usecases. Moving the rest to Q3 to focus more on the devX improvements.