cdk proposal: framework for rich text editors ("draftjs" for angular)

tl;dr https://draftjs.org/ for angular

I've been searching the internets and there is nothing that comes even close to draftjs, which is built on top and requires react. What does it do? It solves most of the [contenteditable issues](https://medium.engineering/why-contenteditable-is-terrible-122d8a40e480) and provides api for people to build their own rich text editors on top of it.

Rich text editor doesn't necessarily mean WYSIWYG textarea, it can help with anything from mentions, hashtags to replacing text emoticons with images etc.


Some of the most popular draftjs plugins can be found [here](https://www.draft-js-plugins.com/) and [here](https://github.com/nikgraf/awesome-draft-js), it should give you an idea what can be done with it.

worth reading:
- https://code.facebook.com/posts/1684092755205505/facebook-open-sources-rich-text-editor-framework-draft-js/
- https://medium.com/@rajaraodv/why-draft-js-and-why-you-should-contribute-460c4a69e6c8
- https://medium.com/@rajaraodv/how-draft-js-represents-rich-text-data-eeabb5f25cf2

I think this could be a great fit for CDK, given that you are eventually planning on creating WYSIWYG anyway.. what do you think?

@jelbourn @mmalerba @kara @andrewseguin @DevVersion @crisbeto

Start by reviewing the Draft.js resources and the Angular CDK context described in the issue, including the linked editor and plugin references. Define the proposed Angular integration, API scope, and acceptance criteria before implementation; the work is done when the framework design and project fit are agreed.

Written by the indexing model from the issue text.