Add support for `Page.wait_for_function`

We're looking to do something that would depend on Playwright's [page.waitForFunction](https://playwright.dev/docs/api/class-page#page-wait-for-function). Specifically, the recommended method for [testing a print dialog](https://playwright.dev/docs/dialogs#print-dialogs) in Playwright uses this functionality. Is that something you'd be open to having?