Add Rust -> Kotlin interop and an example.

[Yury-Fridlyand]

stateDiagram-v2
state "interop/lib.rs" as Rust
state "interop/babushka.udl" as UDL
state "babushka.uniffi.rs" as uniffi.rs
state "Native Lib" as lib
state "Autogenerated Kotlin bindings" as kotlinsrc
state "jar (Platform-dependent)" as jar
state "Kotlin/jvm" as kotlinjvm
state "java/jvm" as javajvm

Rust --> uniffi.rs : uniffi
UDL --> uniffi.rs
uniffi.rs --> lib : Rust Compiler
uniffi.rs --> kotlinsrc : uniffi
lib --> jar
kotlinsrc --> jar
jar --> kotlinjvm
jar --> javajvm

Loading

A resulting jar is platform dependent. It contains a native library and required jvm classes which can load and use it.
A client library/app which uses it should have following dependencies loaded to make things working:

    implementation "net.java.dev.jna:jna:5.8.0"
    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.8.20"

Workflow is copied from BDK: https://github.com/bitcoindevkit/bdk-ffi/tree/master

TODOs:

• Add platform name to the jar file name
• Make dependencies transitive or shadow
• Confirm that we can copy/reuse code from BDK