Add a toggle for the experimental WebGPU mode addon

Increasing Access

One of the first-party addons we build with p5.js is p5.webgpu.js. This is still experimental, but we're actively looking for people to test it out and give feedback and possibly contribute. In the next p5 version, we will have items in the reference that are exclusively for WebGPU mode. It would be great to give them an easy way to try it out via a toggle like we have for our compatibility addons or p5.sound.

Feature enhancement details

• We should make sure to label it as experimental -- we do want people to test it out, but for the purposes of providing feedback and getting involved, as we expect APIs to change. We want to set the right expectations.
• In the same way we let you link to a specific p5 version via a URL param, could we also let you start with the WebGPU addon enabled via URL param? This would help us be able to link to a starting sketch from the p5 website.
• WebGPU mode also requires using async setup and await createCanvas(w, h, WEBGPU). Possibly overkill, but one could maybe try to change that in the code too.

Start by tracing the existing compatibility-addon and p5.sound toggles, along with the URL parameter used to select a p5 version. The change is done when an explicitly experimental WebGPU option can be enabled from the editor and via a URL parameter, with the required WebGPU setup behavior addressed or clearly scoped.