Add HTML-in-Canvas

[foolip]

Specification

Explainer: https://github.com/WICG/html-in-canvas

Spec issue: whatwg/html#10650

Description

This enables drawing HTML elements to canvas.

Documentation

MDN docs aren't created before something is close to shipping.

Demos in https://github.com/WICG/html-in-canvas/tree/main/Examples

Browser support

In development in Chrome.