Provide properly compiled modules for Open UI extension library

Right now `dist/ui-extension.min.js` has all the packed code in one bundle. We assume that it's ES5 module but at the same time, it contains async/await statements came from `emittery`.

Requirements here should be:

• Transpile all the dependencies for the target file as well as source code.
• Generate proper ESM module for modern builds.

A possible solution here would be a migrating to `rollup` and generating targets with relevant flags.