Signals polyfill + pat-bind two-way databinding pattern

[thet]

This adds the new pat-bind pattern for two-way data binding using the not-yet-ready-specified TC39 signals specification in a custom polyfill.

pat-bind allows for declarative two-way data binding:

    <select class="pat-bind" data-pat-bind="key: color">
      <option value="red">Red</option>
      <option value="green">Green</option>
    </select>

    <span class="pat-bind" data-pat-bind="key: color; value: ::text"></span>

NOTE: event TC39 signals is not ready yet, it is used in preact, lit. The specification is meant as a foundation for any reactive framework out there.

https://github.com/tc39/proposal-signals
https://github.com/proposal-signals/signal-polyfill
https://github.com/maverick-js/signals
https://github.com/preactjs/signals
https://lit.dev/docs/data/signals/