feat: support ar in webxr

[xiaoiver]

🤔 This is a ...

• New feature
• Bug fix
• Site / Document optimization
• TypeScript definition update
• Refactoring
• Performance improvement
• Code style optimization
• Test Case
• Branch merge
• Other (about what?)

🔗 Related issue link

#1664

💡 Background and solution

参考 Three.js 的用法。提供默认的 ARButton：

import { ARButton } from '@antv/g-webgl';

const $button = ARButton.createButton(canvas, renderer, {});
container.appendChild($button);

点击后进入 AR 模式。

📝 Changelog

Language	Changelog
🇺🇸 English
🇨🇳 Chinese

☑️ Self Check before Merge

• Doc is updated/provided or not needed
• Demo is updated/provided or not needed
• TypeScript definition is updated/provided or not needed
• Changelog is provided or not needed