Add support for Android Native builds

[lukewarlow]

Currently Kotlinx-rpc doesn't seem to support Android native, I have a use case where I would want to use the core of the library (codegen, client/server declaration and the krpc protocol) inside a kotlin/native binary running on Android.

For my use case I don't need the ktor stuff as I'll be writing a custom a transport.

[lukewarlow]

Fwiw my use case is a multi-process application where the main UI process is kotlin/jvm, but the other processes will be kotlin/native. Android will be the only place to use JVM anywhere so the norm would be kotlin/native for every platform.

I'm looking to use kotlinx-rpc for the IPC system with a custom KRPC transport that uses a variety of underlying mechanisms (e.g. XPC on macOS/iOS). So it would be good for even just the core codegen and kprc protocol to support androidNative.

[Mr3zee]

@lukewarlow thanks for the use case! I'll see how hard it would be to support it quickly