Add wasmJs target [WIP]

[luca992]

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This isn't quite working yet, but started adding support for wasmJs. It will build, but generated code for wasmJs doesn't work because wasmJs only supports calling js code in top level functions:

Calls to 'js(code)' should be a single expression inside a top-level function body or a property initializer in Kotlin/Wasm.

Also, requires an updated moko-graphics with wasmJs added

It could also probably be cleaned up to share more code with the js target.