These methods are safe to call while the page is still open, or when it is
already closed. Works in remotely connected browser as well.
Also makes video.path() to throw for remotely connected browser.
Under the hood migrated Download and Video to use the common Artifact object.
We might not ever get the "download finished" event when closing the context:
- in Chromium, for any ongoing download;
- in all browsers, for failed downloads.
This should not prevent closing the context. Instead of waiting for the
download and then deleting it, we force delete it immediately and reject
any promises waiting for the download completion.
