Adding some emulated canvas support.

Hi,

After viewing the Deno 2.0 anoncement video, I tryed to use observablehq's samples in deno Jupyter Notebooks.

some samplkes use canvas, and so do crash.

by implementing some ugly code I can make canvas's dependent code to works, so it's posible to use an EmulatedCanvas2D to make canvas works in linkdom.

the question is: Can a canvas like can be integrated to the project ?

for reference there is a deno Notebooks of plot-mandelbrot-set:

import * as Plot from "npm:@observablehq/plot";
import { document } from "jsr:@ry/jupyter-helper";
import { createCanvas, type EmulatedCanvas2D } from "https://deno.land/x/canvas@v1.4.2/mod.ts";

function mandelbrot(x: number, y: number) {
  for (let n = 0, zr = 0, zi = 0; n < 80; ++n) {
    [zr, zi] = [zr * zr - zi * zi + x, 2 * zr * zi + y];
    if (zr * zr + zi * zi > 4) return n;
  }
}

const old = document.createElement;
document.createElement = (...args: any[]) => {    
    if (args.length === 1 && args[0] === "canvas") {
        let realCanvas: EmulatedCanvas2D | undefined;
        const canvas = {
            height: 200,
            width: 200,
            getContext: (drv: string) => {
                realCanvas = createCanvas(canvas.width, canvas.height);
                return realCanvas.getContext(drv);
            },
            toDataURL: () => {
                return realCanvas?.toDataURL();
            }
        }
        return canvas;
    }
    return old.apply(document, args);
}

Plot.raster({fill: mandelbrot, x1: -2, x2: 1, y1: -1.164, y2: 1.164}).plot({aspectRatio: 1, document})

Start at linkedom's document.createElement entry point and review how the issue's EmulatedCanvas2D example supplies canvas elements and contexts. Determine the integration scope and compatibility requirements, then validate that the Observable Plot Mandelbrot notebook can create a canvas and render successfully.