[REQ] [Kotlin] Specifying visibility modifiers

[skydoves]

Hello Team,

I'm curious if there's a way to specify visibility modifiers for the generated code, particularly for classes, methods, and properties.

We've been making use of the Explicit API mode feature in Kotlin to enforce clear visibility modifiers, and it would be fantastic if we could ensure compatibility with this feature.

[hamorillo]

Another one here with the same case. It would be a great feature!

[arcadii-meister]

Apparently, this feature has been available for some time, thanks to this PR. However, it supports only setting the internal visibility modifier by using this configuration:

openApiGenerate {
    generatorName = "kotlin"
    ...
    additionalProperties = mapOf("nonPublicApi" to "true")
}

On the other hand, it should solve the explicit API mode compatibility.