[Kotlin]] add support for binary response

[revmischa]

Add missing support for handling binary responses in Kotlin clients.
It would be a lot better to use InputStream for the response type mapping, could use some advice on how to achieve that.

More discussion at issue: #7204

@jimschubert , @dr4ke616 @karismann @Zomzog @andrewemery @4brunu @yutaka0m

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[wing328]

e: /root/src/github.com/OpenAPITools/openapi-generator/samples/client/petstore/kotlin-jackson/src/main/kotlin/org/openapitools/c
> Task :compileKotlin FAILED
lient/infrastructure/ApiClient.kt: (121, 23): Unresolved reference: BufferedWriter
e: /root/src/github.com/OpenAPITools/openapi-generator/samples/client/petstore/kotlin-jackson/src/main/kotlin/org/openapitools/client/infrastructure/ApiClient.kt: (121, 38): Unresolved reference: FileWriter

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':compileKotlin'.
> Compilation error. See log for more details

Shippable CI reports the above error. Please take a look when you've time.

[revmischa]

Imports fixed. Not sure what's with the CircleCI error, looks like a transient issue to me

[wing328]

All tests passed. If no further feedback on this PR, I'll merge it over the weekend.

[revmischa]

I think my solution is not a very good solution. We shouldn't write out tempfiles IMO, we should pass the InputStream handle back to the caller. I was hoping to start some discussion on how to achieve that because I couldn't figure out how to change the type mapping only for the response.
I think the response type should be InputStream or something similar, but want to leave the request type as File because it already has support for transmitting files. It wasn't clear to me how to change the type mapping for the response while leaving the request type mapping as File.

[wing328]

I think the response type should be InputStream or something similar, but want to leave the request type as File because it already has support for transmitting files. It wasn't clear to me how to change the type mapping for the response while leaving the request type mapping as File.

What about using InputStream for both response and request ? In other words, we'll change the type mapping to map binary (format) to InputStream.

I'll put the merge on hold.

[revmischa]

I think this would have to be changed and it would break existing users https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-okhttp/infrastructure/ApiClient.kt.mustache#L100

[wing328]

Upcoming version v5.0.0 is a major release and it's ok to include breaking changes without fallbacks.

[wing328]

Closed via #9284