Add support to generate Kotlin file

[bmarty]

Gradle scripts can now be written in Kotlin, and even if it's possible to generate properties file that gradle can read, it would be nice if pkl was able to generate Kotlin files.

Possible solution:

Create a KotlinRenderer class, which will implements ValueRenderer and add kotlin in the list of supporte format for the eval command.

We would probably need an option to provide the package name, so that the generated file can be moved to to it's target directory and be compile out out the box.

I would be happy if command like:

pkl eval -f kotlin --package-name a.package.name [a pkl file]

generates a Kotlin file with the package a.package.name.

Thanks!

[HT154]

Similar to #972, such a renderer could be implemented in-language and published as a package.