Better TypeScript + Scala.js integration

[xerial]

Although ScalablyTyped makes easier to build facade to use TypeScript libraries in Scala.js, mapping types between Scala.js and TypeScript is not so fun.

• Using JS ecosystem like Vite.js with Scala.js is no problem. It works like a charm.

• Can we have a better approach, such as using Scala.js code (e.g., Rx, RxElement, RPC client) from TypeScript side so that we can leverage more JS ecosystem? ScalablyTyped is the opposite direction.

• async - await in TS -> RPCClient call support

Related https://www.scala-js.org/doc/interoperability/export-to-javascript.html