Add user.copy/user.paste

This example is from Puppeteer's docs to copy text:

```js
await browser
.defaultBrowserContext()
.overridePermissions('', ['clipboard-read', 'clipboard-write']);

// The clipboard API does not allow you to copy, unless the tab is focused.
await page.bringToFront();
await page.evaluate(() => {
// Copy the selected content to the clipboard
document.execCommand('copy');
// Obtain the content of the clipboard as a string
return navigator.clipboard.readText();
});
```

Since it is so complicated, maybe we should implement `user.copy()` that does all this automatically. Paste probably is also as complicated, so maybe `user.paste()` too.