Follow up of issues #2021 and #1472 to add support for Shadow DOM.

More and more apps are being built with Micro Front End architecture in mind, which means components including editor experience are delivered through as a web component, which means, Shadow DOM.

Cisco had been leveraging quill in Contact Center cloud enterprise solution, and now is moving to MFE architecture.

I will be opening a simple PR on behalf of Cisco to address it, please let me know if quill team would have bandwidth to review it within the next 3-4 months, it would help greatly!